183 Voltages Off a Bit

[ValveStorm]

New 183 build seems OK in OD mode, but has squealing in clean mode
Voltages seem a bit off from the layout on v1 and v2

v3 pin1 - 282v (s/b 302v)
v3 pin6 - 288v (s/b 307v)
v2 pin1 - 185v (s/b 207v)
v2 pin6 - 111v (s/b 204v)
v1 pin1 - 281v (s/b 206v)
v1 pin6 - 263v (s/b 207v)

[ValveStorm]

The clean mode squealing gets worse when I engage the PAB relay.
The 3 switches on the front have an effect along with the volume level.
I did the jumper on the Rock/Jazz switch different than the layout to agree with one of the schematics. I also made PAB relay board adjustments to accommodate the AGB relay boards.

[Structo]

Can you show a picture of your power supply?

I'm thinking it needs bigger dropping resistors.

Usually we want around 190v on V1 plates.

200v on V2 plates

and around 300v on the PI plates.

The #183 reportedly had higher voltages across the amp.
Are you running EL34's?

The Rock/ Jazz switch does lower the volume in Jazz mode.

The measurement on V2 pin6 is suspect, might try a different tube there.

[Deric]

Do the V1 voltages change at all in OD mode?

Is the OD entrance grounded in Clean mode?

Double check that the cathode cap/resistors on V1 are grounded - and correct values. Pull V1 and measure resistance from 3 and 8 to ground. While you're at it measure from pins 1 and 6 to the B+5 node.

Would probably be a good idea to take those measurements with and without the OD relay engaged. (power on but in standby - or use a battery to activate the relay).

[ValveStorm]

Thanks you guys so much!
Yep, I had grounded the OD input eyelet next to where the v1 ground should have been connected! Doh!

Things are much better now... squeal seems to be gone.
Yes, running EL34s... I only have 2of 4 in there now.

Voltages now:
B+ - 459v
B+3 - 432v
B+4 - 312v
B+5 - 304v
v3 pin1 - 284v (s/b 302v)
v3 pin6 - 289v (s/b 307v)
v2 pin1 - 175v (s/b 207v)
v2 pin6 - 171v (s/b 204v)
v1 pin1 - 183v (s/b 206v)
v1 pin6 - 166v (s/b 207v)

[Structo]

Much better voltages.

Of course you need to have four power tubes in to have the proper
load on the supply and resultant voltages.

Have you tried different preamp tubes?

That V1 pin 6 voltage seems low.

what does s/b mean?

Here is a voltage chart of my 100w ODS
My amp has high plate/ cathode resistors and 80's style power supply.

Here's a blank chart you can print out and use.

[ValveStorm]

Here is the voltage chart with all 4 EL34s installed.
The s/b above stands for "should be" based on the voltages shown on the 183 layout.

Thanks for your help!

[martin manning]

You could try a different tube in the V1 spot to see if the plate voltages even out. If the tube were perfectly balanced, the 150k/2k2 side would be about 5V higher at the plate.

Grid voltage on V3 must be measured at the junction of the 820R and 1M resistors to get a meaningful result.

Your power tubes are not very well matched, but you can swap V5 and V6 to get the two sides balanced.

B+ is low re the layout. If you want to bring the preamp voltages up a bit, decrease the 3k on the power supply board to say 2k2. Try that out for sound by tacking a 10k 1W across the 3k.