Preamplifier in Mahogany

Hi!

A couple of weeks ago I showed a preamplifier in black/silver color combination. Today I'd like to  present a similar preamp combination in mahogany frames.

Phono section on the left, next the linestage and the two external power supplies on the right:

A view from the side:

The circuit and tube choice is the same as the previous preamp.

Some more views:

And here some photos of the previous black preamp in it's new home:

In this system the preamp drives a pair of 211 mono amps.

Which in turn drive a beautiful speaker based on an Onken cabinet with GOTO drivers.

Best regards

Thomas

Music: Daft Punk, Random Access Memories

Hi!

I was excited when Daft Punk released it's new Album this year, but didn't really like it at the first listen. So it went into the record rack where it stayed unplayed for a while. Only recently I pulled it out again and the more I listen to it, the more I like it.

With Random Access Memories, Daft Punk created a new album which sounds very different from their previous ones yet their unique style is still present. The album opens with a rather soft track 'Give life back to music' which sounds very retro 70ies Disco. Funky guitar, the voice modified with a vocoder. The second track, 'The Game of Love' continues like that, maybe they over did it with the vocoder here. In the third track, the last on side one of LP 1, Giorgio Moroder appears as guest.


Moroder was a pioneer of electronic music in the 70ies and influenced many musicians, obviously including Daft Punk. In this track Moroder narrates about how he started his career. Again funky 70ies style guitar in the background with some bass. Very cool and totally non-commercial. A nice tribute by Daft Punk to one of their role models. Side two of the first track starts with a ballad like title called 'Within' again with heavily vocodered voice. The second track 'Instant Crush' starts similar to the first one, but gets a bit faster with more aggressive guitars towards the end. Nothing really special. Side two ends with the best title of this side. 'Loose Yourself to Dance'. Not as much over use of the vocoder. Funky guitars. This is also a title which is played often in the radio.

LP 2 starts off very differently with atmospheric electronic sounds which resemble the early synthesizer music style of the 70ies. As electronically altered voices start to narrate, some sounds kick in which could be off the sound track of a 70ies Science Fiction Movie. Then the title turns into a ballad, dominated by vocals. A cool and relaxing track. The second title on this side 'Get Lucky' is probably the most played as it was in the charts as well. Funky guitars and a smooth driving rhythm, very listenable.

The last side starts with some orchestra which reminds of some typical film sound tracks. It later changes into synthesiser music which resembles the sound of Daft Punks Sound Track of Tron Legacy. The side continues with a mix of very different tracks. Although the overall music style is rather non-commercial, Daft Punk seems to have hit a certain nerve with this album since it is selling quite well.

The album was released on Columbia/Sony Music. The pressing quality of the vinyl is excellent. Very low noise. The recording quality is very good as on other Daft Punk albums. The record comes with a beautiful booklet:

An album worthwhile to add to the collection. It might take several listens before you appreciate it. Get the vinyl and savor it!

Best regards

Thomas

Guest Post: Robert's 6CB5A Amplifier

Hi!

Quite recently I had the pleasure to meet Robert. He built a version of the 6CB5A amplifier and wrote up a nice story about it. Now I am happy to hand the word over to him:

Greetings VinylSavor readers, I'm Robert from Switzerland and thanks to Thomas, I'm allowed to ramble a bit about my build of the 6CB5A based amplifier of which you can find various versions here. Before telling you about my experience building this amplifier, let me briefly tell you a bit about me.

I'm not what people would call an an old school audiophile, who only swears by vacuum tubes and technology from the past when "everything used to be better". I'm not the modern times equivalent either, who can spend hours trying to find out differences between power cords or USB cables... Actually by the usual definition I'm maybe not an audiophile at all: music just happens to be very important to me. So how did I get into this amplifier building endeavour then?

I've been tube curious for a long time and fascinated by electronics in general (I've got a computer science engineering background) and after going through several iterations of commercial solid state equipment for my two music systems I got more and more interested by the insides of the components and why some choices of topology, components or design were made. This usually brings one very quickly to the DIY "scene" which to me was like falling in the rabbit hole leading to Wonderland.

I suddenly discovered a wealth of smart people who were not only very knowledgeable in electronics, but had a real passion for exploring circuit topologies, components or ideas which were unusual, forgotten or commercialy not interesting for mainstream Hifi vendors. I was hooked.

I came across Thomas' web site during one evening while I was reading articles about LCR phono stages and spent hours reading his articles. The more I read, the more I wanted to build some components myself. I thought that ideally I should have a preamp, a phono stage and a power amplifier to make a complete home made system. However, at that point, I had zero practical experience and not even a soldering iron... so where should I start? I decided to start with a tube preamp kit using a PCB so that at least I could learn how to solder first. This was a success and after hours of patient assembly, it worked from the first time! The phono stage followed shortly after and, soon I've been able to listen to my first vinyl on a home made phono preamplifier!

At that point things became addictive: I had several options in front of me for the power amplifier and everything became possible: 300B, 2A3 or 45, interstage transformers, exotic rectification systems, etc... - all this fueled by the myriad of projects on Thomas's site. Since I already owned both a 2A3 as well as a 300B amplifier (commercial ones) I decided that I wanted to try something a bit more unusual: enter the 6CB5A amplifier.

I started discussing the options with Thomas and settled for my 6CB5A to be configured like this:

• Stereo build
• Interstage transformers
• Full wave tube rectification
• Lundahl iron
• I would design and build my own enclosure

After discussing the possibilities over email I decided to go and pick up the parts directly (it's a only a 3h drive). I spent the afternoon with Thomas and we had a really nice time discussing amplifiers, vacuum tubes and V8 engines. As you can see, it's all about the music!

The first thing one should know about Thomas' amplifiers is that choke filtering, massive power transformers and the necessary hardware are quite heavy. The weight of the wooden crate I left with that day should've clued me about the fact that I would have to manipulate it on my desk during assembly but at that point I was just happily going back home with my new toys.

The enclosure design

The first step needed was to design an enclosure that fitted the 40cm x 40cm footprint I already used for the preamplifier and phono stage. An additional constraint was that the box would have to be closed so that if necessary components could be stacked on top of each other. This is where I started to realise that a stereo version with an integrated power supply would become a monster of an amplifier. After lots of trial and error with the panel designer CAD application, I converged on the following design:

• A panel would split the enclosure horizontally at about 1/3rd of the height and components would be attached to it
• The PSU section would get it's own panel and would 'float' above the power transformer at the front
• The top panel would have an opening with a plexiglas insert to leave the interior visible
• The rear panel would have an opening open to let the heat evacuate from the back

Panel 1: this is the power supply panel.

The bridge rectifier is built with the four 6AX4 TV damper tubes. To the left and right are the filtering chokes and towards the edges are the filter capacitors. Grounding has to be carefully routed from here to avoid ruining the excellent filtering offered by the LCLC filter.

Panel 2: the middle panel inside the enclosure (front is at the bottom). The various components are placed so that wiring is minimized and the big cut out allows the power transformer to be screwed to the bottom plate.

The PSU panel is mounted above the power transformer on aluminum profiles so that the 6AX4 tube sockets are about 1.5cm above the top of the power transformer. On each side are the additional, per channel, LC filters. The interstage transformers are in the middle of the panel and very close to the 6N7 tubes. Finally the output power transformers are at the back of the chassis nearby the outputs and the 6CB5A tubes. It's all very tight in there and I was really hoping I didn't make any mistakes on this very expensive panel!

All the smaller holes between along the middle of the panel are used to screw metallic standoffs for the various other components and also for running the ground cleanly across the amplifier from back to front.

Panel 3: the rear panel with the opening that allows hot air to escape.

The inputs use Neutrik sockets which are rather expensive but of excellent build quality, AC input filtering is done through a Schurter IEC inlet with integrated fuse holder. For safety reasons, all the metallic parts of the chassis are grounded at the IEC ground. Signal ground can be floated or not using the ground lift switch.

Panel 4: the front panel with the power button. I like clean and pure layouts so the front side is very plain. The power button is made by Schurter and has an integrated LED dot to indicate operation.

In addition to the above, there are top and bottom panels and the plexiglas window that will be shown further down in the final build pictures. All the aluminum panels were professionally made on a CNC in 4 mm anodized aluminum. Given the complex layout, the cost of the enclosure is relatively high and contributes to about 40% of the total bill of materials.

Building the amplifier

My components kit came entirely from Thomas (iron, sockets, tubes, resistors, capacitors) and I just had to add:

• Speaker connectors
• RCA input connectors
• IEC inlet
• Enclosure and associated hardware (aluminum profiles, screws, standoffs, washers, etc...)
• High quality wire: I used Alphawire only, 20 AWG / 600V for most of the build, 16AWG for the OPT to speaker connections, and solid 16AWG for the grounding - signal wire uses smaller 24AWG.

I started the assembly with the power supply board:

The LCLC filter can be seen below, with the wiring for the 6AX4 rectifier bridge. The aluminum profiles are cut at the appropriate length so that the bottom of the rectifier tube sockets are just above the power transformer.

I verified several times my connections to make sure that the anodes and cathodes of the diodes were connected correctly to avoid a smoky situation later on... Between the numerous filament wires and the bridge wiring, it's very easy to make a mistake. Of course due to the AC filament supply, those wires need to be cleanly twisted together to avoid hum contamination. The ASC caps are a pleasure to work with due to their very practical connectors that allow up to four connections to be soldered.

Note: the solid wire for the ground bus can be seen in green running along one side of the PSU panel and the cap on the right is the power supply 'exit' to the rest of the amplifier.

Next on the list came the main board with the remaining components: given that I didn't ask the panel edges to be milled clean they remain very sharp and will cut fingers at the first opportunity. That is the reason for the ugly tape around the corners of the panel which stayed until the end of the build:

I began the assembly by installing the tube sockets, screwing in all the transformers and doing the filament wiring. The blue heat shrink tubing is used to insulate the screws and nuts used to attach the tube socket to the board from the nearby electrical connection.

I made a mistake during the assembly of not using washers between the ceramic tube socket and the aluminum panel which leads to the result below. Morale of the story: sockets are fragile.

Several hours later (yes I'm slow), the main panel is almost completely wired:

It's very clear that the whole construction is completely mono on each side with only the power supply that's shared but decoupled through additional LC filtering (upper left and right chokes and caps). The other aspect that I like about this circuit is that no capacitors are used to connect the amplifier stages. The lower two capacitors on each side of the 6N7 and 6CB5A tubes are the 'ultrapath' connected capacitors.

A couple of additional close-ups of the main panel:

The next steps involve connecting the inputs and outputs from the rear panel to the rest of the circuit. This is the rear panel with the connectors installed:

The bottom panel is now needed as well with the power transformer. Thomas includes rubber bumpers in his kit to securely connect the transformer while decoupling it from the chassis so any eventual vibrations won't affect the rest of the amplifier.

First power up and basic circuit testing

Now that the main building blocks are ready, they're all brought together and like the kits I built previously I try to avoid problems by going through the following checks:

• Inspect visually the circuit by carefully following connections on the schematic and on the board after all the soldering is completed. I caught a few nasty mistakes by just doing that simple step.
• Make basic measurements in various places without power connected: Thomas offers a very good step by step pre-flight check for the 6CB5A amplifier in his articles and I've used that to double-check my own build. Please note that his measurements are for a capacitor coupled amplifier and some measurements won't match if it's transformer coupled version instead.
• Power up the filaments to verify that tube filaments are alright
• Power up the PSU and B+ without connecting it to the rest of the amplifier. I use a resistor load to make sure that the voltage doesn't go too high for the capacitors.
• Power up the amplifier with B+ connected.  Here Thomas' power transformer is a fantastic asset: it has configurable output voltages and this is extremely useful when starting a circuit for the first time by being able to feed it a lower voltage.
• Finally power up with a high B+ and measure with an oscilloscope.

Filament and B+ all good - the first time power up is always quite exciting! As you can see I've temporarily wired the power transformer with a fused test lead that allows me to avoid having to touch anything during the first power up. It's very important to ensure that chassis metallic parts are properly connected to the IEC inlet ground before applying any high voltage.

It's alive! This is the first test of the amplifier output and it works nicely! I'm testing it with a low B+ (the red line sitting at about 180V) and in blue it's the speaker output showing the amplified sine wave coming from the signal generator. I immediately checked the other channel and it's working great.

Since I'm not very patient, I bumped up the power transformer voltage to 400V and directly connected it to my speakers - it had to play some music now :-)

I don't like to talk about how amplifiers "sound" because it's very personal and it depends a lot on the components around it but the first things I noticed are that it's very quiet, and it had serious bass. This was a bit unexpected because I was running it on my low sensitivity (92db/W/m, 4 ohm) speakers and I would have expected a single ended amplifier to struggle a bit with only 8-10W.

That is simply not the case, it sounds clean and solid with a deep musical bass foundation - a really good surprise! Worth noting too (but that's totally expected): this amplifier has a relatively low sensitivity and depending on the source may require a real preamplifier with gain instead of the modern equivalents which mostly perform attenuation.

Once I was happy that everything worked as it should, I completed the build by adding the wooden side panels and the remaining bits and pieces.

Completed 6CB5A amplifer with the bamboo wooden panels and the top plexiglas window:

Top view: in the evening it looks like a Christmas tree - very nice!

Rear view on the 6CB5A tubes. A lot of heat is pouring out from the back confirming the decision to leave a large opening as being a good one. Tubes can be replaced from the back without opening the top of the enclosure. I'm running the power transformer at 525V secondary (primary on 240V) and the plates of the 6CB5A are fine when I ran the amplifier at my place. However when connected to higher mains voltage (at a friend's place where mains are 10-15V higher for some reason) the 6CB5A plates started glowing a deep red meaning that I will have to rewire the power supply to the 500V secondaries at some point.

Top view: very nice view on the tubes and the inside. However one must make sure not to drop anything inside the case!

Summary and what's next?

I really had a lot of fun building my first power amplifier based on the 6CB5A kit. On top of it I learned a lot and the results are way above my expectations sonically speaking: it's a really great amplifier and in many ways I prefer it to my commercial 300B amp (an Allnic). If I were to do it again, I would probably consider separating the power supply from the amplifier chassis to make it less heavy to move around. This is something that Thomas does for most of his designs and it makes a lot of sense.

I've tried the 6CB5A in various setups with both high sensitivity (101db/W/m) as well as low sensitivity speakers, with solid state and tube preamps and I came to the conclusion that for the price it's extremely good. Even when not taking price in consideration, it's a fantastic amplifier design that's well in the league of commercial components costing 4-5x more. And then there are options that can make it even better: my 6CB5A uses all Lundahl iron but other more exotic magnetics can be used to further improve the performance. 

Given the sound quality, I'm now thinking about pairing it up with a preamplifier that's sonically better matched than my home made 6SN7 preamp, and one of my next projects will involve Thomas' 6AH4 based job with transformer volume control.

Thank you Thomas for sharing with us your passion - it's really appreciated!

- Robert

Thanks Robert for the great write up and congratulations for the beautiful amplifier!

Best regards

Thomas

New Power Transformers - Neue Netztrafos

Hi!

It is has been a while since I presented my line up of power transformers. Since then I added 5 new models for different applications. I also added some transformers with center tapped secondaries since many people asked for them. Here is the line up.

Es ist schon eine ganze Weile her, seit ich meine Netztrafos vorgestellt habe. Inzwischen gibt es 5 neue Varianten, für verschiedene Anwendungen. Es gibt jetzt auch Netztrafos mit Mittelabgriff auf der Sekundärwicklung, da ich öfters Nachfragen für solche Transformatoren bekommen habe. Hier jetzt die ganze Trafo-Palette:

The older models are in the second row. All data for these can be found in the first transformer post.
The new models in the front row share the same general characteristics: Grain oriented cores, vacuum varnished, double screening, outer flux band, tapped primary for 220/230/240V. Models for North America also available (115/120/125V).

Die älteren Modelle sind in der hinteren Reihe. Alle Daten dazu sind in dem ersten Trafo-Artikel zu finden. Die neuen Modelle haben den selben Grundaufbau: Kornorientierte Bleche, vakuumgetränkt, doppelter statischer Schirm, Fluxband, Primäranzapfungen für 220/230/240V.


Transformer for 211/845 amps - Trafo für 211/845-Verstärker

The first transformer on the left is meant for 211 or 845 amps. For these it needs to be used with a bridge rectification scheme. It has 3 separate 6,3V heater windings to supply the heaters of a bridge consisting of 4 TV dampers. The heater windings are brought out as isolated wires. The secondary voltage is 525-500-475-450-0-450-475-500-525V/300mA.
This allows the selection of a secondary voltage from 900 up to 1050V in 25V steps. If the same tap is used on either side of the winding, the center tap can be used to derive half the voltage from the main output, for example to power the driver stage. Of course the transformer can also be used with a center tap rectifier scheme for other purposes. This transformer is a big beast. It barely fits under the 150mm transformer cover.

Der erste Trafo vorne links auf dem Foto ist für 211 oder 845 Endstufen gedacht. Für diese Anwendung muss eine Graetzbrücke als Gleichrichter verwendet werden. Dafür gibt es 3 separate 6,3V Heizwicklungen um eine Brücke aus 4 TV-Damper-Dioden zu heizen. Die Heizleitungen sind als isolierte Drähte rausgeführt. Die Sekundärspannung beträgt: 525-500-475-450-0-450-475-500-525V/300mA.
Dies erlaubt Sekundärspannungen von 900 bis 1050V in 25V Schritten. Wird jeweils die gleiche Anzapfung an den beiden Enden verwendet, so kann vom Mittelabgriff eine zweite Spannung abgeleitet werden, die die Hälfte der Hauptspannung beträgt, z.B. für die Treiberstufe. Der Trafo kann auch in einer Gleichrichterschaltung mit Mittelanzapfung verwendet werden, für andere Endstufen. Dieser Trafo ist ein ziemlicher Brocken. Er passt gerade so unter die 150mm Trafohaube.


Transformers with center taps for 45 / 2A3 / 300B amps - Trafos mit Mittelanzapfung für 45 / 2A3 / 300B Verstärker

The next two transformers in the front row are meant for 'classic' tube rectifier power supplies and can be used for amps using 45, 2A3, 300B or other similar tubes. They have a high voltage secondary 400-350-300-0-300-350-400V and two heater windings. A 6,3V winding for signal tubes and a 0-5-6,3V winding for the rectifier. A 5V tap was added to enable the use of classic rectifiers like 5U4, 5R4, GZ34, GZ37, etc.The 6,3V tap can be used with TV Dampers like 6AX4, 6AU4. There are two versions, which differ in the current rating: The larger one has a 300mA high voltage secondary. The 6.3V heater winding can supply 7.5A. The rectifiers heater winding is rated at 3A for both. The smaller transformer has a 150mA high voltage secondary and 5A heater winding. All currents are the AC rating. Both versions fit under the 150mm transformer cover. The smaller one of the transformers is a little bit too high so that the 120mm cover does not fit.

Die nächsten beiden Trafos in der vorderen Reihe sind gedacht für Verstärker mit klassischem Röhrengleichrichter. Verwendbar z.B. für Eintakt-Endstufen mit 45, 2A3 oder 300B. Die Hochspannungswicklung ist ausgelegt für: 400-350-300-0-300-350-400V. Es gibt zwei Heizwicklungen. Eine mit 6,3V für Signalröhren und eine 0-5-6,3V Wicklungen für Gleichrichter. Eine 5V Anzapfung wurde vorgesehen für klassische Gleichrichter wie z.B. 5U4, 5R4, GZ34, GZ37. Die 6,3V Anzapfung ist für TV-Damper gedacht wie 6AX4 oder 6AU4. Es gibt zwei Ausführungen, der größere Trafo liefert 300mA auf der Hochspannungswicklung und 7,5A auf der 6,3V Heizwicklung. Die Gleichrichterheizwicklung ist auf beiden Trafos für 3A ausgelegt. Beim kleineren Trafo kann die Hochspannung 150mA liefern und die Heizung 5A. Die Angaben beziehen sich jeweils  auf den entnehmbaren Wechselstrom. Für beide Trafos ist die 150mm Haube passend. Der kleinere Trafo ist ein klein wenig zu hoch um unter der 120mm Haube genügend Platz zu finden.


Transformer for use with bridge rectifier for 45, 2A3 or 300B amps - Trafo für Anwendungen mit Graetzbrücke für 45, 2A3 oder 300B Verstärker

The next transformer in the row got developed for use in 45, 2A3 or 300B amps. It is meant to be used with a bridge rectifier with 4 diodes. The secondary arrangement follows a similar approach as my older transformers. It allows secondary voltages to be selected in steps of 25V from 100 up to 400V. The current rating is 300mA. It has two heater windings 6,3V/6A each. One to be used for the rectifier bridge and the other for signal tubes. For this transformer the 120mm cover is the right size.

Der nächste in der Reihe wurde für die Verwendung in 45, 2A3 oder 300B Verstärkern mit Brückengleichrichter (4 Dioden). Die Anordnung der Sekundärwicklungen ist ähnlich zu meinen anderen Modellen und erlaubt Sekundärspannungen von 100 bis 400V in 25V Schritten. Der entnehmbare Wechselstrom beträgt 300mA. Der Trafo verfügt über zwei getrennte 6,3V/6A Heizwicklungen. Jeweils für die Gleichrichterbrücke und Signalröhren. Für diesen Trafo passt die 120mm Haube.


Filament transformer for 211 / 845 - Heiztrafo für 211 / 845

The last of the new transformers is meant for DC filament supplies for 211 or 845 tubes. One transformer is needed per tube. It has a secondary which can be configured in 1V steps from 1V to 20V. The current rating is 5A. It can be used with choke input filters. The voltage is sufficient to reach 10V at the filament with a LCL filter configuration with two Lundahl LL2733 filament chokes. It fits under the 120mm cover.

Der letzte der neuen Trafos ist gedacht für die DC-Heizversorgung von 211 oder 845 Sendetrioden. Es wird ein Trafo pro Röhre benötigt. Die Sekundärwicklungen können für Spannungen von 1-20V verschaltet werden, in 1V Schritten. Es können 5A Wechselstrom entnommen werden. Mit diesem Trafo kann auch eine Heizung mit Drosseleingansgfilter aufgebaut werden. Die Sekundärspannung ist ausreichend  um z.B. eine 211 über ein LCL Filter mit zwei Lundahl LL2733 Heizdrosseln zu versorgen. Die 120mm Haube ist passend.


Send an email if you are interested in any of these transformers (address to be found under the link Impressum/Contact). I will help to select the right transformer for your application.

Bei Interesse an diesen Trafos bitte email schicken (Adresse im link Impressum/Contact). Gerne bin ich behilflich den passenden Trafo je nach Anwendung auszuwählen.


Best regards / Viele Grüße

Thomas

The Octal Preamplifier Mk3

Hi!

Today's post will show the assembly process of a new incarnation of the Octal Preamplifier line, the Mk3.

Previous versions of the Octal Preamplifier have already been presented on this blog. The Mk1 was the first in the line which got an upgraded version, the Mk2 (photos here). The Mk3 version merges the circuits of the Octal Phono Preamplifier and the Octal Line Preamplifier into one chassis. In order to fit it into a single chassis the simpler version of the power supply has been used without any chokes.

The Mk3 version does not render the Mk1 or Mk2 obsolete. They are different circuits and represent preamplifier implementations at different cost and sound levels. The Mk3 represents the lowest cost version, the Mk1 is in the middle and the Mk2 remains the best sounding (and highest cost) version of the three.

The assembly starts with the top metal plate, here with tube sockets and power transformer mounted:

The tube sockets are mounted with vibration damping rubber elements:

First the heater wiring is done. I decided to leave the line tubes on AC and the phono tubes are heated with DC.  The high voltage AC leads to the power transformer are also in place already:

Next some solder terminal strips get mounted. These will hold all the passive components:

Solder terminals stuffed with all the passives:

The face plate holds on/off switch, volume control potentiometer and the input selector switch. As much as possible is prewired before the face plate is inserted into the chassis:

The same with the back plate, all wires from the input jacks and to the output jacks are already soldered to the connectors. The MC step up transformer is mounted directly besides the phono input jacks:

The MC step up is a Lundahl LL1681. It is connected to two switches, one per channel, which allow selection of the step up ratio between 1:13 (for higher input impedance) and 1:26 for low input impedance and maximum gain. Switching is done as already shown on a spearate MC step up unit.

Front and back plates inserted and ready to be wired up:

wiring all the inputs to the selector switch is the most tedious job during the build process. All input wires are twisted with a ground wire for shielding. This ground wire is only connected at one end. There are separate ground connections for the inputs and the output. One wire for all inputs and one for  the output. These are connected to the ground point of the line stage part.

Mains AC wires are covered with an extra insulation sleeve. Also the input and output wires for protection:

 Wires are purposely not bundled to minimize crosstalk. Looks messy but works better. Now the bottom plate and transformer cover remain to be attached and the preamp is ready to play:

This preamp is the first to use my new transformer covers.

Top View:

The back side with all connections:

Phono input on the left (MC only). Two switches to select between 1:13 and 1:26.  Next three line level inputs and the output jacks. On the bottom left is the ground lift switch.


Some views of the tubes:

The next project will be an integration of this preamp circuit with the low cost variant of the 6CB5A amplifier. This will be a fully integrated amplifier with phono on board. Stay tuned!


Best regards

Thomas