The Amp Garage

Ok, in retrospect it should have been obvious, but the gate of an n channel jfet is a pn junction, normally reverse biased for linear operation.
So yes, it may be feasible to operate a source follower around zero / slight forward bias, to achieve similar effect to a DCCF.

Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? That is, ’direct DC coupled emitter follower’. Was thinking of trying this for a pedal.. I can't envisage how, the effect requires a device wi...

martin manning wrote: ↑Tue May 28, 2024 11:53 am ... If the secondary is open ...

Just to expand, even without an open / intermittent load on the secondary, I think the inductive nature of a regular cab will tend to result in leading edge back emf spikes with a heavily overdriven amp.

... How is this flyback voltage generated. The individual claimed it was from an open circuit on the secondary. I had heard people claim an open circuit secondary leads to shorted turns because the insulation is damaged, but I haven’t heard it affecting the parts in primary. .., As Martin mentioned...

... 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...