The Amp Garage

is the center tap(tan, red) on the chart the only ground on the o t?

That tan/red wire will connect to B+, not ground.

Stevem wrote:The 5f4 schematic I just looked at

Can you post that schematic?

I've been using this "potato masher" 5R4 with 6550s for years in my Sunn Sceptre.

[img500]http://home.comcast.net/~seluckey/amps/sunn/sunn_02.jpg[/img]

V1, V2, V4, and V5 ALL have zero volts on the cathodes. That means none of those tubes are passing any current. Look for a common problem, such as no ground connection for those tubes. Measure resistance from those cathodes to ground. One probe directly on the socket pin, the other on chassis. Proba...

What if you just wanted a Single In for the Power Amp.? Then don't install the preamp out jack. You don't need a two circuit TRS jack. Just a simple switchcraft 12A (single circuit with switch) will do. The preamp will be disconnected from the PI when you insert a plug into the power amp input jack...

I was going to say it looks like a universal PP tranny, with the #4 connection ("B") as the center.

Ah, that makes sense.

It appears to be a single ended OT. AC-15 uses a push/pull output.

This is how I do it. Also works as a passive effects loop. Just be sure to put the jacks before the input cap for the PI.

http://home.comcast.net/~seluckey/amps/ ... vember.pdf

Have you actually built this? No, but some guys over on Hoffman's board have. I have this layout from some where and i have wondered if there would be much of a volume jump when switching from the 1987 to the JCM channels? I have wondered if there needs to be a volume control for the JCM stage? The...

So what happens exactly...that cause a 6.5 VAC winding to read 100 VAC at the tube filament.? The 100VAC reading is a bogus reading. The filament winding no longer has a reference to ground so any voltage reading to ground is bogus. As soon as you connect the filament winding to ground whether by g...

I'm guessing that since I now use v1b for the dark 1959 channel, that some signal from it will leak into the signal going into v2a (stage2 in 2204 and SIR 39). I think this might be ok. But perhaps I should be connecting v2a into the junction of the two 470k resistors after the bright and dark volu...

3) I have an extra triode. It is bothering me. I'm considering two options. The first is to wire it up as the other input stage from a 1959 and make it switchable with a pot mounted switch. The second is to wire up a switchable matchless parallel first gain stage. Thoughts? I like the 1959 option. ...

I WOULD really like to get the power supply behaving as designed before I start modifying for the foot pedal or scrapping the original power supply. I'm starting to think the relays may be the problem. There may not be anything wrong with the electronics. You say you can get the relays to switch. S...

taking the plate supply from after the pi filter

Vox AC-15 does this. All the old Sunn amps did too.

Pierre wrote:I just finished a wreck inspired amp and thought I'd share the schematic with all of you.

There's an error on you schematic that you may want to correct. You have both inputs to the PI grounded.