The Amp Garage

I ran into an issue with EL/KT types and para-phase inverter with the inverting side directly coupled to a resistance divider. The G1 current can throw off the inverter bias. Have to use a blocking cap. 6l6/6v6 don't suffer the issue so you can simplify. A little G1 current is normal under typical c...

I had one of those... the iron is alright... 8417 got me into KT88/90/100/120... I think I remember that they were one of the last USA tubes to be developed, a bit flaky for quality ... might still have the brochure and maybe some knobs.

power supply decoupling,.. Mod the power supply,... it could also be wire dress inside the chassis, double check what and where the longest wire paths
are. I use plastic input jack with its own ground to star as well.

second the old JBL... I know an old fellow who worked vegas back in the day... princeton and a JBL E or K 120.
small clean and loud... he was real particular about his pre amp tube as well, auditioned a lot of tubes.

Ive a couple old cinaudiograph i like and old old jensens are loverly too.

Confirmed... And it works. The cathode bias sets the minimum or cold condition. And a positive fixed voltage is applied at the grids to raise the bias to a hot setting. So instead of LFO signal varying the bias condition It becomes a user contol. Anti bias. This happens as an amp ages as well. Old a...

I know its close. I'd much rather have more as well.

1 12at7
2 12ax7

@ .9A

2 6bq5/el84

@. 1.52A

Tot. 2.42 A

PT 6.3 rating 3A

There are many ways to apply tremolo in an amp. One way is to modulate the grids of the power tubes. But the trade off becomes bias stability of the power tubes. With this in mind I was looking for a trem that was less impactfull. I found this intensity control in some old magnatones with cathode bi...

Thats a thought. The circuit is not much different as far as the tone formation component goes... But to get both channels to play nice and in phase I had to back up the mix component a gain stage and reduce the drive channel output with a Pi attenuator. So... Ceramic and mica's were OK... Poly OK.....

I have a univox on the bench. The client opted to convert the rig to el34 from 6873. Easier to source and more affordable than NOS. I have had to rebuild the bias supply. I went with an ampeg solution. Resistor network off the HV taps on the PT. The problem developing, cascading across the PCB as I ...

Yes yes... Im just stunned that the tone structure seems so reliant on one cap. It seems to pass just the right portion of the upper mid and not the harsh high mids. I've had some traynors over the bench with the same value cap in the same position In the circuit. On a brite switch... Really changes...

I bet its because theyre old leaky crappy parts.

Seems miraculous where its applied.
Cheep poly nichicon for the signal path. No odd values.
One other mica after the clip stage but run of the mill otherwise

Ya.... Its .0014. It wasn't the low end. Its the top that gets me.
Smooth smooth smooth. That circuit can be very aggressive.
The top can be harsh a bit hot with a ceramic or mica.
Somthing about it... Smooth and complex.

Just buttoning up a mod thats based on a JCM 800. I happened to try an old SANGAMO TYPE 33 .001 as the brite cap over the first volume control in the circuit, exploring parts and voicing...... I'm blown away it makes the tone of the rig. I picked the cap out of a box of junk and glad I tried it. Wha...

Reversing the function of the master vol. appears to be the right idea for this application. It becomes an old school mixer. I've played with some doggy master vol. rigs and the first impression was a surprise. I can live with it.. Tone is good even at low and moderate volumes. Get the clean tone vo...