Voltage problems

[badfan]

Guys

Being a 'newbie' to amp building I have been doing OK for my first 4/5 builds but I have a problem that has started on this one that has foxed me.

The symptoms are very simple with all tubes pulled the B+ voltages look correct to the plates on all sockets. No voltages showing up on cathodes etc and everything appears fine & stable.

If I put V1 in and start measuring, the voltage on the tube seems way to high, plate voltages are in the region of 300+ with cathode voltages around 140 in addition I am seeing around 35v on the earth connection?

Because I seeing that 35v+ plus volts on the earth connection it seems to be getting in the signal path?.

It happens with a number of tubes in the same position that are working ok in other amps so I dont think it is the tubes.

If i do the same with V2 i.e. pull all tubes and then just put that one in and measure the voltages again they look way high similar to V1.

V3 looks closer to the correct voltages but again not close enough.

Please note with all tubes in I am getting the standard hiss out of the power tubes / OT etc heater voltage is correct and the heaters are all on etc but nothing is coming out of the pre-amp. If I turn the gain up completely I am getting a squealling noise

In addition I am measuring a what I believe is a high voltage on the earth connection i.e. around 140+.

When I get time later on I will post the actual voltages for viewing but any initial thoughts / tests I should do would be useful?

Cheers
________
Marijuana vaporizers

[Bob-I]

......in addition I am seeing around 35v on the earth connection?

Stop right there. Re-examine your grounding scheme. You should not see a voltage on the earth at all.

[paulster]

......in addition I am seeing around 35v on the earth connection?

Stop right there. Re-examine your grounding scheme. You should not see a voltage on the earth at all.

Exactly, stop! But where are you measuring between to get this 35V? Your ground should be the chassis, and everything ground-related should be connected to this, so there should be no opportunity to read 35V on a ground connection.

[badfan]

Yes i understand that hence being careful. Some more information.

I have 3 ground points in the amp.

1 - Earth ground to the chassis (reads 0 volts)
2- Star Ground A - Bias, OT ground, power cap, power tube grounds (reads 0 volts)
3. Bus bar B - pre amp signal ground, input jack ground etc
- reads 0 (with no pre-amp valves in)

With no tubes in I am getting 419v on the standby switch (off)

Standby on with ONLY power amp tubes in (6v6's) i get the following
B+1 = 405
B+2 = 403
B+3 = 403
B+4 = 403
B+5 = 402

V1 V2 V3
1 - 400 1 = 399 1 = 399
2 - 0 2 = 0 2 = 0
3 - 0 3 = 0 3 =
6 - 399 6 = 399
7 - 0 7 = 0
8 - 0 8 = 0
Bus bar B = 0 volts

V4 V5
1 - 0 1 - 0
3 - 405 3 - 406
4 - 406 4 - 405
5 - -33 5 - -32
6 - 406 6 - 405
8 - 0 8 - 0



With V1 & power amp tubes in (6v6's) i get the following
B+1 = 407
B+2 = 391
B+3 = 380
B+4 = 368
B+5 = 356

V1 V2 V3
1 - 305 1 = 364 1 = 375
2 - 126 2 = 124 2 = 110
3 - 128 3 = 126 3 = 120
6 - 283 6 = 377
7 - 110 7 = 110
8 - 128 8 = 120
Bus bar B = 126 volts

V4 V5
1 - 0 1 - 0
3 - 404 3 - 403
4 - 403 4 - 401
5 - -33 5 - -32
6 - 403 6 - 401
8 - 0 8 -

As you can see just with 1 pre amp tube in the whole pre amp circuit seems to be getting DC coming in?

Cheers
________
Vapir Oxygen