Tube Amp Archive

Thanks a lot for your replies ! While your at it spin that OT 90 degrees. Yes, I did it :wink: A few notes are here: https://www.vintage-radio.net/forum/showthread.php?t=28068 Unfortunately, the circuit drawing is AWOL. Thanks for the link Stephen. I draw the schematic, it's really easy. After readi...

Hello, A friend had this amp in his garage for years, and he just decided to have it restored. When he first showed it to me years ago, I had a search on the web and found only one article. But I can't find it anymore. If I remember correctly, Axis amps were hand made by a man near Brighton, and a v...

I got the answer ! :) They are Orion Tubes, but in fact, this is rebadged Sovtek production (exactly the same EL34-G). So not very good tubes :( They also had some Polam and Telam ones. From the watfodvalves website : "Orion Radio valves were originally a brand name of the Tungsram factory of Hungar...

Hello,
Someone just brought me an amp with unusual EL34. I've never seen this funny logo before.
They are labeled EL34 G, and look like Sovtek EL34G (base, mica, getter). But does anyone know the production of these tubes ?
Thanks for your help.
Cyril.

trobbins wrote: ↑Mon Jun 03, 2019 7:02 am TG9686 detailed info in linked thread:
https://groupdiy.com/index.php?topic=72605.0
https://groupdiy.com/index.php?topic=72609.0

Thanks for the links, but it's about the TG6556, used on Hiwatt DR504. Or did I miss something ?...

Output Transformer is Raa of 4K to suit a pair of EL34 according to this: https://picclick.fr/PARTRIDGE-output-transformer-50-Watts-4k-Ohm-123290414878.html Cheers, Ian Thanks Ian, and thanks to you all. I found the tests result, but as you stated trobbins, I'm a bit puzzled with the measurements. ...

Hello, I'm looking for the specs of some Partridge transformers. I have a set of PT, OT and choke from a Dan Armstrong 60 head, but I can't find anything about them. PT is TH2025. OT is TG9686. Choke is TH9688. I'm ok with the PT (2x440VAC, 2x3.15VAC), but I'd like to know the primary impedance of t...

Thank you all for your replies and advices. Those heater wires are running parallel with the OD wires. I would try lifting them up and see if that makes any difference, or try shielded wire. Thanks Aaron, the wires next to the heaters are not signal but B+ wires. But it could also cause some noise, ...

Swapping the OT primaries should result in a big squeal or no squeal. So it's uncertain what you actually did. :shock: :shock: :shock: :shock: ???????????? Forget this OT, pleeaaase... I buid amps for 20 years, so I know this problem of OT leads. Yes it produces a big squeal if it's wired incorrect...

If you said that swapping OT had no impact then that's not right either because if you had it right and swapped there'd be a very clear impact Of course swapping the leads has an impact, but it did not solved my problem. And yes, I will try to make a sound sample. I want to show you a small example...

The one I'm working on.
I use terminal strips now, and my amps are dead quiet, no hum at all. MF resistors on OD, shielded cable, but it doesn't seem to suit the OD design. Oscillation on this one.

Pics !
Here is an old design, from an amp that I built 15 years ago. The wiring is not that good, carbon comp resistors, no oscillation.

If you dont know where the oscillation is coming from how would you identify if its coming from the OT or not? Based on new information I also believe this is the commonest problem ever to happen on any amp with some NFB. Disco the NFB. Swap the darned OT wires and hook the NFB back up where it was...

I do not think the author is talking about the natural hissing of the tubes. Most likely, this is some kind of positive feedback between the stages. Yes, that's it ! :) Thanks. It's a feedback, not from the OT, but I don't understand where that comes from. I did all the things you mention : swappin...

Big oscillations are often caused by a bad lead dress. Find the #124 pics on http://thesubjectmatter.com/dumblearchive.html and compare your wiring to what Mr Dumble did on his. Yes you're right. I also did some changings in the wirings. In fact I use this OD schematic for years, and now I use very...