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Saturday, March 8, 2014

Tube of the Month : The 45 (revisited)


The 45 has already been covered in a Tube of the Month post. Two sets of mono blocks with the 45 got finished recently and it is one of my all time favourite tubes. So it deserves a revisit. This post will mostly be about the different variants. For all technical aspects about the 45 see the original Tube of the Month post. Now get ready for some 45 porn.

The 45 was introduced in 1929  as UX245. It was very popular as output tube in radio sets and has been manufactured in an abundance of varieties by many manufacturers. Probably the most famous is the RCA:

This is the more modern ST shape, with printed base:

Earlier tubes had engraved bases:

RCA Victor 45 with the Nipper box:

Cunningham made by RCA:

Beautifully engraved base:

Different version:

This heap of RCA Cunningham 45s look the same at first sight:

But some are slightly different in their internal construction:

Many tubes have labels from the stores which sold them:

The earlier Cunningham CX345:

RCA globe shape 45:

The top:

Slightly different version with a little glass piece for adjustment of the electrodes:

The base:

Tung-Sol 45:


Different Sylvania 45s:

Sylvania globe UX-245:

Philco, made by Sylvania:

Zentih, probably also made by Sylvania:

General Electric:


Fivre 45 made in Italy:

Two australian 45 radio tubes made by Amalgamated Wireless Valve Co:

Arcturus 45 in the beautiful boxes with the observatory motif:



Majestic G-45:

Two different ST shape Silvertone tubes:

Earlier Silvertone UX-245:

In this tube the getters starts to flake off a little. This can be an indication that somebody tried to reactivate the getter by applying heat through a flame from the outside. It can also came off all by itself. The tube tests fine:

National Union ST shape 45s:

NU produced the 45 over a long time, which is apparent from the changes in styles:

Engraved bases on the older types:

Printed on the later tube:

Also differences in internal construction:

Globe shaped National Union NX-245:

Now let's have a look at the internals of a 45 tube. Don't worry, I wouldn't salvage a good tube for this. This unfortunate Philco 45 got dropped on the floor:

Removing the remaining glass:

Close ups of the top showing the suspension of the filament:

Bottom of the electrodes:

The holder of the getter material:

Removing the plate:

Since the top suspensions got cut off the filament lost it's shape:

Close ups:

Next some odd brand tubes.

The first one is quite peculiar and I only ever came across one of these. A ST shape 45 with  ceramic base:

Not sure if this is genuine and was manufactured like this or if somebody rebased a 45. It bears no brand markings. Could be RCA, here a photo of the top:

Gold Seal 45:

Wards Super Airline:

Globe shaped 45 with Super Airline branding (without the Wards):

This one is shorter then the typical globe 45, here a comparison:

Commander 45:

De Forest 445:


Sonatron 45:


Hy Ray:




And finally the most peculiar brand name which I came across: 'OK':

I'd like to finish this post with some 45s in operation:

Here a 45 in a new amp which will be shown in an upcoming post:

Stay tuned!

Best regards



  1. Hi Thomas,

    Great 45 photos.. The smaller Super Airline might be an ST14 bottle, as opposed to the more common larger ST16's?

    I hope to see an 801A amp soon. Maybe even in PP, for around 6-7 Watts.


  2. Hi!
    The Super Airline is a ballon shape, not ST.
    A 801A/801A amp is in preparation...stay tuned...
    801A is not real well suited for Class A PP as it would require an output transformer with a huge primary impedance. Nothing really suitable is available

    Best regards


    1. Hi Thomas,
      I disagree on the PP application. 20-22K plate-to-plate with suitable operative conditions can be very very good. Effective plate resistance (i.e. the composite tube) in PP amps is lower than the corresponding PSE configuration and more importantly constant across the whole operative range if properly implemented. The latter is not really the case of SE amps where Zout is signal dependent.

    2. Hi!
      I would rate a 20-22k primary already as very high. I personally like higher load impedances. Sure it is doable but I would use tubes with lower plate resistance for PP.


  3. Hi Thomas,

    Ahh, yes.. I didn't recheck the the Super Airline photos before posting. Globe 14's maybe, if there's such a thing.. 45's are also suitable for linestages / headphone amp..

    Yes, you are right. Except maybe for custom wound PP trans, although quite difficult to wind I suppose.. Can't wait for that 801A SE amp.


  4. Beautifull post for gorgeous sounding tube. On the technical note, how is globe type to st type with respect to microphonics and noise? Any special care needed?

    1. Hi predrag,

      see my post about globe tubes for some description about differences:
      I have not encounter noise issues with globes. Some can be a bit microphonic.

      Best regards


    2. Thomas, a very nice collection of 45 tubes! Since you have experience using both the 45 and 46 in similar topologies, I am hoping you can provide some comments on the different sound qualities of these two tubes. Thanks.

    3. Hi!

      I never compared both tubes in exactly similar amps. Both perform very nicely. The 46 gives a bit less power. Anyways the circuit will probably have a larger influence on the sound result as the choice between 45 or 46. Both are excellent

      Best regards


  5. hi Thomas -

    ok, where's the real porn? do I need to send you some? I am talking:

    Raytheon 245 box plate, embossed plate globe
    Rogers 45 mesh plate globe
    Arcturus blue globe 145
    EML globe and mesh plate 45s
    Perryman 45
    Sonatron 45 mesh plate globe
    Sylvania mesh plate globe 45
    Cardon/Sparton 45 globe (Solid and mesh)

    break out the good stuff for us! ;-)


  6. Hi Ed,

    Send them across and I will make another post about the 45 showing these tubes :-)


  7. ok! working on it... ;-)

    1. Cool, I'll do another one on the 45 showing the real hardcore stuff then ;-)

  8. The white ceramic 45 could be a Raytheon, by the way.

  9. The globe 45 had some mesh anode make by Marathon I remember..