6AQ5 Mini JCM800

[randalp3000]

Still on the Marshall and small amp kick. So this time going to do a JCM800 as soon as I receive my PT and chassis.

I'm going to start with the stock preamp but might try some of the Soldano hot rod 50 values.

If you have any thoughts please share
thanks
randal

[statorvane]

Tone Lizard has some good pointers on JCM800 preamps here, including several to increase the preamp gain.

http://tone-lizard.com/Ultimate_JCM800.htm

I built a clone for my son, and we wound up snipping the bright cap and replaced the treble peaker with a 68Kohm resistor. We were looking to beef up the amp at lower volumes and these two mods did the trick. This was the 50 watt version - EL34s.

[10thTx]

I built this 6AQ5 amp w/VVR and enjoyed it a lot. Fun amp to play. With the 5879 V1, it was a pretty touch sensitive amp and had a reasonably FAT tone to it.

IF I built it again, I'd use a different tone stack and a PPIMV.

with respect, 10thtx

[randalp3000]

thanks for the replies.

got the chassis punched this mourning and did the turret board the other night. I should of had my PT and some other parts friday but the weather slowed them down. They should be here tomorrow hopefully.

[statorvane]

I built this 6AQ5 amp w/VVR and enjoyed it a lot.

What is the purpose of the 12V zener diode between gate and source of the MOSFET?

[martin manning]

Excess G-S voltage (on a transient say) will destroy the FET. The Zener limits that to 12V as a safety precaution.

[randalp3000]

Got it fired up last night.

It's got a weird, loud buzz when I turn up the master. I must have screwed something up. Hopefully be able to mess with it some more tomorrow.

edit, I did swap out the power tube 100r cathode resistors for 1r's

[xtian]

Three out of four of the eCaps on your board look crushed. Is that just normal crimping?

I see you have a faux 100R heater center tap. Make sure you don't ALSO have a heater CT grounded. That would cause a nasty buzz.

[randalp3000]

thanks for looking,

I'll look at the caps when I get home but I think they are all good.

PT does not have a center tap for the heaters.

also I did swap out the power tube 100r cathode resistors for 1r's

[TimmyP1955]

I built this 6AQ5 amp w/VVR and enjoyed it a lot.

What's the MOSFET for?

What's the mid thingie above the treble pot?

[statorvane]

The MOSFET is a cathode follower - eliminates a triode.

The thing above the treble pot is a single pole double throw (SPDT) switch - appears to adjust the range of the treble cap.

[billyoung]

I know this is old topic but was there any sound samples ??

bill

[billyoung]

heres yet another mini marshall I am working on