ARS filter caps, what to expect?

[BesaMoogie]

Please always make a plan as to what you’re going to do in the chassis when it’s live, do that plan, and if it doesn’t work as you expect, turn it off, drain the caps, and reassess with another plan.

I`m doing that. I have a test probe hocked up to a high wattage resistor and a clamp (everything insulated) to drain the caps everytime I work on the amp

 

[Kapo_Polenton]

Tubes are biased in both amps at about 60-65% within the variance of the duet/quartet. Of course, this is taking the different PVs of the amps into account. Preamp is not tweaked and the NFB resistor is 100k wired to the 4ohm tab. At one point I had it wired to the 8ohm tab.

The clone started out with all CC resistors and Mojo Dijon caps and was worlds apart from the original 2204. The bottom end and response reminded me of my Dual Rectifiers, but maybe a bit tighter? Changing the coupling caps to a mix of Sozo and Phillips MKT 344 and changing the pf caps from SM to ceramics did bring me much closer tone, but not feel wise.
I am currently changing the CC resistors in the B+ supply line as well as the anode plate resistors for Beyschlag MF resistors. I started early in the preamp and work my way through it. Slowly, the punch is coming.

But there`s still a layer of rather dark harmonics instead of grind that makes the bottom end of the JCM800 2204 so percussive and fast responding

Transformer is your next big bet! ( which goes back to my original suggestion) They are a big part of the vibe. I have an 82 800 that has a darker feel to it next to my homebuilt 2204 with classic tone transformer which is snappy , tight, fast.

 

[BesaMoogie]

Transformer is your next big bet! ( which goes back to my original suggestion) They are a big part of the vibe. I have an 82 800 that has a darker feel to it next to my homebuilt 2204 with classic tone transformer which is snappy , tight, fast.

Yeah, probably you`re right. But it`s kind of a costly step I try to circumvent if possible.

 

[BesaMoogie]

Filter cap brand isn’t going to solve your problem.

First thing I’d check with your symptoms is preamp voltage. That makes a huge difference in feel, saggy vs punchy. Check it at the PI dropper just after screen supply on each amp.

Also compare voltages at every node after the PI dropper, PI plates, V2B plate, etc, etc down to v1.

I did measure the voltages across both amps before. You can have a look in the chart attached. It`s worth to mention, that the measurements were done with CC resistors, which usually tend to have higher resistance, so it`s possible that the voltages are higher now with the more accurate MF resistors.
Push and feel improved after changing the CCs for MFs in the B+ support line and anodes of V1. I will go further down the preamp and change the rest of them.

 

[SpiderWars]

Measuring the voltages in the preamp, the clone had about 5 volts less on the plates.

The clone has a PV of 450V and an OT made by Dagnall. The JCM800 2204 has a lower PV of 390V, but still feels more percussive.

So the power supply is different in some way? Because the clone has ~60v higher PV but ~5v lower preamp voltages?

Sometimes it seems if a stage is getting slammed too hard it sounds less crunchy and can get boomy/slow. This might sound counter-intuitive but try putting a 1M resistor across the gain pot (making it 500k) and see if that takes it in the right direction. Easy to try.

 

[BesaMoogie]

So the power supply is different in some way? Because the clone has ~60v higher PV but ~5v lower preamp voltages?

Sometimes it seems if a stage is getting slammed too hard it sounds less crunchy and can get boomy/slow. This might sound counter-intuitive but try putting a 1M resistor across the gain pot (making it 500k) and see if that takes it in the right direction. Easy to try.

Thanks for the advice.
The JCM 800 has one 10K resistor less in the B+ support line. That’s why the preamp voltage is more or less the same as in the clone

 

[Bardagh]

I am using standard leaded solder. Heater wires are 18 AWG, AC wires are 20 AWG and signal wires are 22 AWG, all non-stranded push back cloth.
One thing I changed was using shielded coax wires from input to V1B and the gain pot to V1A.
I read somewhere, that the grounded chassis can influence signal carrying wires by acting similar to a cap and dampening highs. Maybe I am loosing some of the Marshall grind that way?

Changing the input wire to a shielded coax did not result in any perceptible change to the high end/grind of my 2204, however I did not change the wire from the gain pot as it was not necessary. The change in unwanted noise from just the input wire was massive, making the amp easily as quiet under gain as anything else I have.