70's Sonic (pa) Bass amp

[bbirling]

I am working on a 70's Sonic what Appears to be a pa amp possibly. It runs (4) 8417 and (4) 12AX7's Control panel shows Volume-Treble-Presence-Bass-Reverb and a Bright Switch. The back panel has 2-4-8-70 volt Speaker outs and a FS for the reverb.

Right now it's output is very low volume. One 12ax7 in question is the one in the middle of the picture.
Voltages-(1)302(2)0(3)2(4)H(5)H(6)0(7)0(8)0(9)0

I do not have a schematic for this amp and can not find one.

Hopefully we can start there.

[Platefire]

From the vacant holes in the chassis, this amp seems to have been pretty heavily modded. I would suspect the tubes first and try known good tubes first to see if that corrects it. I always clean pots and tube sockets with contact cleaner on any old amp I get. Platefire

[PRR]

> (6)0(7)0(8)0

There's stuff on those pins, so it isn't un-used.

Find where Plate (probably pin 6) is supposed to be getting power from, and find why it isn't getting it.

[bbirling]

While I really didn't have the time to reverse engineer this thing I did find this link with the same Sonic Head in question. The Kern looks almost identical from the outside but the chassis is much different on the inside.

http://vintageamps.com/plexiboard/viewtopic.php?f=11&t=87506&p=992851

[HotBluePlates]

... The Kern looks almost identical from the outside but the chassis is much different on the inside.

A little different, but not very different. Tube sockets and wiring appears the same, best I can tell from their low-res photo.

You amp has additional filter caps inside the chassis, while theirs appears to have 2 extra can caps mounted approximately where your Cornell Dubilier filter caps are.