The Amp Garage

... I'm worried that the pops might be quite loud... Pop / thump noises are usually caused by - a change in DC voltage charging or discharging a cap (which causes a momentary change in DC voltage) I don't think that a loud pop is likely to occur in that schematic, unless one of the output valves ha...

those who have switched between two larmars have simply used two 500k stereo pots in parallell, which gives about the same resistance as single 250k stereo pot. Instead of the 2m2 security resistors on the 250k you may need to adjust the value of the security resistor. but don't be too mechanincal,...

There's the V3 LTP a-a snubber cap on the 2203/4 rolling off a bit of high end.

There's a tendency with master volume amps not to turn the master up full, so perhaps instability with the 2203 doesn't get noticed? Any gain boosting mods to the 2203/4, eg at the 2nd stage cathode, often necessitate stability mitigation, eg anode to cathoe or anode to grid cap at the input stage. ...

Should I leave the thermal fuse and ground changes as is or remove them? 'Ground changes'? You mentioned that the ground pin had been removed from the mains plug. That certainly needs sorting, eg fit a new plug. Replacing the mains cable might be more difficult, as a big bertha iron might be needed...

johnnyreece wrote: ↑Tue May 14, 2024 6:16 pm ... According to the manufacturer, these are 450VDC working; 500VDC surge. ...

I guess their definition of surge voltage capability may end up being more arduous than your amp subjects them to?

... My electrolytics are rated for 450V, but with a 5U4, my B+ nears 500V while warming up. Is this okay, or should I get higher rated caps? Their short term surge voltage rating might be up to 20% above their max working voltage rating. So as the near 500V will only last for 20 seconds or so, a ti...

I have read multiple times on this forum and other forums that the preamp should be grounded at the input jack. I have posted about this previously. I am the outlier here. I never ground at the input jack, yet, I get good results. I was taught by someone (online) who I respected, to run a buss from...

V1B cathode voltage of 5.5V is bad.

As I recall, Fender were making valve amps with pcb mounted pots from the early 80s.

Especially if there's a valve rectifier, I prefer to add a HT fuse in the CT return to 0V common of the HT winding. That seems to be more common in early 60s amps, such as JTM45 or AC50 https://el34world.com/charts/Schematics/files/Vox/Vox_ac50.pdf In this arrangement, F500mA works fine with my JTM4...

Yes, Michael does great work, and very reasonably priced.
I just sent him a photo of a sketch with dimensions, but Im sure he can work with CAD files.

I'm not keen on the OT being so close to the input stages. A screening plate can help to keep things stable in that type of scenario so perhaps think about how one might be squeezed in before everything is set in stone.

do these amps draw more current than a jtm45? I think so, due to the much lower impedance OT, but then so does a JTM50, yet the same spec mains transformer got used, for the early production at least (as I understand it). As I recall, the T&B mains transformer was a bit smaller than a JTM45 type. P...

If you send the duff mains transformer to Luke at Transformer Equipment, I think he could backwards engineer it and build a clone, for a fraction of the MM price. But yes, a good JTM45/50 mains transformer should be electrically fairly similar. A friend has a dead T&B MkII that needs a lot of work, ...