• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

45 Tube amp project

I am collecting parts to do the diy project published in glass audio magazine 1995. "Single ended Glory" by Eric Barbour. After reading reviews and posts concerning 45 tube amps, I am certain that they have the qualitys I am looking for. I own modded Klipsch Lascalas,(104 db/1w), so the 2watt output should be sufficient for my medium to small listening room.
Has anyone built this project? In the article, Mr. Barbour says that expensive single ended opt's are unnecessary, as the 25 ma. drawn by each tube won't saturate a decent 30 watt push pull opt.
He says any unit of 30 watts with 4 to 6kohm plate to plate resistance will be fine. He used the iron from a Sansui receiver,(1000a), and could discern little difference when he subbed in a friends Audio Note single ended opt.
I see transformers rated at 5kohm primary at various parts suppliers. Is 5kohm primary the same as 5kohm plate to plate?
I have built many projects, but this is my first tube amp.
It seems simple, won't be that expensive, and should sound great by all accounts. I am now using 2a3 monoblocks.
I understand the dangers involved in tube high voltage and feel secure enough to build it. Any help appreciated.


2001-12-12 7:42 am
I am not familiar with the exact circuit that you are refering to but Ihave built and am using a 45 tube amp. Driver tube is 5842 and uses a 1:2 interstage.
The #45 sounds wonderful! Better than a 2A3 that I also built and definitely better than the PP34 that I built. I am not using any exotic parts and it definitely sounds better than my SE2A3 which I spent much more on due to the expensive resistors etc.
to 45drive45

Thanks for the info!
Can you reccomend some good,( and affordable), output transformers for the 45 amp. What output iron did you use for your 45? I would like to use something a little better than the Hammond 125se for $28.00 each, but less expensive than the Magnequest exo-45 which is very expensive but supposedly fantastic with 45's. Something under $200.00 per pair?


2001-12-12 7:42 am
For the opt I am using a rebuilt WE iron from Japan. It looks horrendous ! haha. Here in Singapore there are a few diy folks who have use Lundahl OPT with great success. Its not very expensive but obviously it depends if you have easy access to it. Personnaly I have used Lundahl and it sounds good and not THAT expensive. Over here its about S$195 or about US$110 each. Only thing about the Lundahl its not potted so its really ugly displaying unless you can get a nice cover for it. In all my new amp, I try to place everything under the chassis and only leave the tubes on top..sometimes a capacitor or two! Decided to go with a minimalist style on the outside but under the chassis its loaded. The main reason was to hide those ugly Lundahl OPT and Interstage and Power Trans.
Have fun building

siu sin man tho

Disabled Account
2002-11-08 4:55 pm
hong kong
I use 417a to push 45 already.
later use 6C45 interstage to puch 45.


  • ·ó¤ù 043.jpg
    ·ó¤ù 043.jpg
    64.3 KB · Views: 2,677
45 output transformer

I've built this circuit several times. The Hammond 125ESE and 125E are both good sounding within their modest price range, but have significant limitations in bass. If you really hope to get the best from a 45, spend a bit more on the iron.

If you really need to keep under $200/pair, look into the Hammond 1628SE or One Electron UBT-2

If you can swing a bit more, the Electraprint BE5KB ($260/pair) is a great choice - very sweet sounding. At a bit higher price the Magnequest DS-050 ($360/pair) are also very very nice.

siu sin man tho

Disabled Account
2002-11-08 4:55 pm
hong kong
this is the finish outlook of my 417a push 45 se amp.
I use tango iso xe20s c-core output.
I can choose 3.5K or 5K to change the sound quality.
I use this amp to push my 1970's klipish la scala.
1970's still use alnico magnet.
also I use this amp to push my AER too.




  • tango's 061.jpg
    tango's 061.jpg
    67.1 KB · Views: 2,633

siu sin man tho

Disabled Account
2002-11-08 4:55 pm
hong kong
hi 45 driver 45,

for your project. I try 1:1 & 1:2 interstage already.
If the driver tube had enough power pls try to use 1:1.
The 1:2 winding will loss a little bit of high frequency air.
I compare it in my AER to test. It made me more easy to hear the different.
For the structure, 1:2 winding will cause the increase of capacitance so the high freq will los more than 1:1.
pls see the photo, I use this speaker to hear the high freq different.




  • photo 7.jpg
    photo 7.jpg
    75.6 KB · Views: 2,140
Re: 45 output transformer

The-Planet said:
The Hammond 125ESE and 125E are both good sounding within their modest price range, but have significant limitations in bass.

That's certainly not true in all circumstances. It has a primary inductance of 10.5H at 80mA - so it will be significantly better at half that current, or lower. I would bet a 45 would be less than 2dB down at 20Hz.
I've used them with a 71-A that has an Rp of 1170 ohms, and I can tell you that the bass is not lacking in any way.


Don't get me wrong, the 125E and 125ESE are surprisingly good given their modest cost. I listen to a 6EM7 amp which uses the 125ESE every day in my office.

I've built the simple 45 design referenced here. I've also built a version of Gordon Rankin's "Bugle 45". I spent many weeks living with the Bugle 45 circuit on a breadboard before I committed to a final design. I had a good selection of output transformers on hand to audition. I listened to Tango U808, Hammond 125E, Hammond 125ESE, Hammond 1628SE, Electraprint BE5KB and others. Speakers were Altec A7's.

With a 46 at 22ma or 45 at 36ma there really is something missing on the Hammond 125ESE's lower end. IMHO, in a direct comparison with better iron it was quite audible.
Re: 125E/ESE

The-Planet said:
With a 46 at 22ma or 45 at 36ma there really is something missing on the Hammond 125ESE's lower end. IMHO, in a direct comparison with better iron it was quite audible.


I don't doubt you think you hear a difference - but that doesn't do us much good, does it? Do you have any measurements? They would be most helpful.

45 Transformers...

Joel -

I did try all of the transformers in the identical circuit. I had the amp on a breadboard with a heathkit regulated power supply, lots of audiophool grade wire clips and careful parts layout ;) for a long time and went bach and forth between output transformers. Several friends participated in the listening as well.

Ok, so it wasn't completely blind - but I had no vested interest in the outcome. I also can't explain my impressions based on any "science".

In any case, we've probably beat this to a respectable pulp. Some time if you find yourself in New England give a yell. I'd be happy to repeat the "experiment" over a few beers.

On another note, what does your 71A circuit look like?

If i'm not mistaken you tried some better caps and liked them. Did you measure any improvements that correlated with the better sound? Is it so unreasonable to expect that better iron also sounds better? Or do you honestly think that there is no difference at all between different cores, different winding geometries and different insulation materials? Lots of gullible audiophiles falling victim to the 'TANGO CONSPIRACY' :) ? I also doubt that a db or two is important but that's not where the real difference is.




diyAudio Senior Member
2002-08-21 1:20 am


Sorry, I just don't buy that a dB or two difference at 20Hz is even noticable.

There's more to an OPT than just the frequency response last time I looked.

And FWIW, I don't want one that's a few dB down at 20KHz already...even more importantly, I don't want one that's down a few dB at 20Hz.

Maybe not everyone discerns a difference but I do nonetheless.