strange v1 voltages

[JimiB]

I was checking my volatges tonight and I noticed that V1a is really low.
I tried several different tubes and some were better but both the eh's I tried were the same. I am running a 325-0-325 pt and 220K/150K on both tubes. Ideas?
V1a-149
V1b-210
V2a-209
V2b-219
V3a-327
V3b-308
HT+A-440
HT+B-436
HT+C-429
HT+D-333
HT+E-326

[tele_player]

I'd check the plate and cathode resistors, to see that they're the correct values, any error on the wiring of V1, shorted bypass cap? What's the voltage at pin 3 on V1?

[DaveBo32]

I would check the tube socket itself, I had a similiar problem. The socket had a green corrosion from the flux in the solder. This cause a poor connection with the tube, which resulted in low voltage values. Pull the tube out and check the voltage again. Good luck.

Dave

[odourboy]

And finally, check the tube. I had two Sovtek 12AX7s that both gave me similar voltages to that. I was pulling my hair out trying to find the error when there was none. I put in a decent brand of tube and voila! Problem fixed. (Sovteks in garbage.)

Let us know who wins!

[dogears]

The solution will be one of the ideas offered... So, check the socket, plate/cathode resistor and bypass cap.

As an aside, your voltages are too high anyway. Is this a Dlite? If so, increase the first dropping resistor to a 2.2K and reduce the FET simulator from 220K to at least 180K.

[JimiB]

O.K.
with no tube in V1 the voltages are
V1A - 355
V1B - 357
I tried 6-8 different tubes and the best is a GT12AX7WB that gives me
V1A - 177 plate
V1A - 2.25 cathode
V1B - 217 plate
V1B - 1.57 cathode

I checked the plate resistor 220.8K
the cathode reisistor 3.262K
the bypass cap 4.77uf
tried it with a new bypass cap - no change
i re-tentioned the tube sockets - no change

Any ideas?

Scott - I will drop the FET sim resistor to a 180K and bump the first dropping resistor to 2.2K

[DaveBo32]

Maybe try some contact cleaner. I went through the same bull #$%. I ended up replacing the socket after I tried all the common scenario's. That worked for me. Good Luck.

https://tubeamparchive.com/viewtopic.ph ... highlight=

[dogears]

Hi Jimi,

Are you sure about your values? The V1a should have the lower cathode voltage. Are your resistors swapped? Did you check continuity??

O.K.
with no tube in V1 the voltages are
V1A - 355
V1B - 357
I tried 6-8 different tubes and the best is a GT12AX7WB that gives me
V1A - 177 plate
V1A - 2.25 cathode
V1B - 217 plate
V1B - 1.57 cathode

I checked the plate resistor 220.8K
the cathode reisistor 3.262K
the bypass cap 4.77uf
tried it with a new bypass cap - no change
i re-tentioned the tube sockets - no change

Any ideas?

Scott - I will drop the FET sim resistor to a 180K and bump the first dropping resistor to 2.2K

[tele_player]

Tube in, verify that the grid voltage is 0 V DC?

[odourboy]

Tube in, verify that the grid voltage is 0 V DC?

Good question!! Or could wild oscillation result in those kind of voltage readings?

[Bob-I]

V1A - 177 plate
V1A - 2.25 cathode

This is just wrong. Focus in on this area. You checked the cathode cap and resistor, did you try new one's? Did you double check the ground connnections?

[JimiB]

Are you sure about your values? The V1a should have the lower cathode voltage. Are your resistors swapped? Did you check continuity??

checked continuity and it is good from the board conection to the socket where the pins connect.
Double and triple checked values.
Disconnected the wire that connects the V1A plate to the tone caps - no change.
took reading with 2 different tubes they are
EH12AX7
pin 1: 142v
pin 2: -0.16v seems to vary up to -1.32v. with the 22k input r. disconnected, it went up to -2v
pin 3: 2.65
pin 6: 209
pin 7: 0.001
pin 8: 1.62

GT12AX7WB
pin 1: 177v
pin 2: -0.038v to -1.1v
pin 3: 2.164v
pin 6: 213
pin 7: 0.00
pin 8: 1.6

[JimiB]

at the input jack where the 1M resistor connects to ground and where the ground wire connects had no solder.
I had just replaced the 3.3K with another 3.3K and I couldnt figure out why the grid wasnt "seeing" ground.
Damn I feel like an idiot.

V1A 199
V1B 212

I will get to the fet sim. resistor and replacing that first 1K dropping resistor with a 2K.

[JimiB]

Scott - with 2.2K as the first dropping resistor and 150K as the FET sim. voltages are:
V1A 194
V1B 200
V2A 200
V2B 204
V3A 316
V3B 306

as soon as those 110K reisistors get here I will swap the 82K/100K PI resistors with 110K and 120K as you suggested. Thanks for the help!

[dogears]

Much better!! You can also try a 3K instead of the 2.2K

That may be even more betterer. LOL

How does it sound? Should be WAY better!

Scott - with 2.2K as the first dropping resistor and 150K as the FET sim. voltages are:
V1A 194
V1B 200
V2A 200
V2B 204
V3A 316
V3B 306

as soon as those 110K reisistors get here I will swap the 82K/100K PI resistors with 110K and 120K as you suggested. Thanks for the help!