Troulbleshooting my 5e3: Bias reading 65mA

[Tom Phillips]

...The meter with air between shows 0.L (zero.L) infinite.

Right. Infinite. That ".L" was the important missing clarification. "0.L" means "overload" in meter speak.

...With those two parts still out of the circuit (completely), pin 8 to the chassis is reading just under 50 ohm now.

That's a problem. It should read O.L. Something else is providing that 50 Ohm path. If you can find and fix that then you can reinstall the cathode resistor and cap and the amp should work properly. Or at least better. Time to take a really close look at your work in that area and the condition of the tube sockets. Did you verify that measurement with the 6v6 tubes removed?


Making progress,
Tom

[Jonny toetags]

That's a problem. It should read O.L. Something else is providing that 50 Ohm path. If you can find and fix that then you can reinstall the cathode resistor and cap and the amp should work properly. Or at least better. Time to take a really close look at your work in that area and the condition of the tube sockets. Did you verify that measurement with the 6v6 tubes removed?


Making progress,
Tom

That reading was taken with the all tubes in the amp. I will take it again without them tonight.
So I should focus on the powertube sockets?
I'll report back tonight when i work some more on it.

[Jazz P Bass]

Right. Infinite. That ".L" was the important missing clarification. "0.L" means "overload" in meter speak.

I always took "O.L." to mean 'Open Line'.

50 ohms, 50 ohms.
Heater connection?

[Tom Phillips]

...So I should focus on the powertube sockets?...

In this case not necessarily the sockets themselves but start at pin 8 of each 6V6 socket and trace out anything that is connected.

I'd expect that there is now only wiring going to the eyelet board since you have removed the R & C.

Work one step at a time.
Connect your meter and re-verify the 50 Ohm reading from pin 8 to the chassis.
Lift the wire end at the eyelet board to isolate the areas. If the reading pin 8 to chassis stays at 50 Ohms then look for a miswire to the tube sockets. If the reading pin 8 to chassis is now "0.L" then measure at the eyelet board connection. If that spot measures 50 Ohms to chassis then follow all the connections on that side looking for a miswire.

Work methodically and take your time and write clear notes of what happens at each step.

Can you post photos of the project?
Also post a copy of the schematic you used. Does your version include elevated heater circuit fed from the 6V6 cathode or does it show just the R&C connected to pin 8?

Good Luck,
Tom

[Jonny toetags]

In this case not necessarily the sockets themselves but start at pin 8 of each 6V6 socket and trace out anything that is connected.

I'd expect that there is now only wiring going to the eyelet board since you have removed the R & C.

Work one step at a time.
Connect your meter and re-verify the 50 Ohm reading from pin 8 to the chassis.
Lift the wire end at the eyelet board to isolate the areas. If the reading pin 8 to chassis stays at 50 Ohms then look for a miswire to the tube sockets. If the reading pin 8 to chassis is now "0.L" then measure at the eyelet board connection. If that spot measures 50 Ohms to chassis then follow all the connections on that side looking for a miswire.

Work methodically and take your time and write clear notes of what happens at each step.

Can you post photos of the project?

Good Luck,
Tom

I forgot to mention, that when i pulled out the cap and resistor, i also disconnected the wire that goes from pin 8 on the 6V6 to the board. That wire was disconnected when I measure the 50 ohm reading.

I'll definitively post pics when i get home.

[g1]

One or the other or both parts (if they measure bad) need to be replaced. Then try the amp again with another set of 6V6s. Parts do experience early failure. It could have been the resistor, the cap or one of the power tubes.

I forgot to mention, that when i pulled out the cap and resistor, i also disconnected the wire that goes from pin 8 on the 6V6 to the board.

That would seem to leave only the 6V6's and there sockets. Had you at any time tried some other 6V6's in there?

[Jonny toetags]

That would seem to leave only the 6V6's and there sockets. Had you at any time tried some other 6V6's in there?

Nope, just the brand new set of Tung Sol's. If it's the tubes I'm really going to be pissed.
If I pull the tubes and still measure a resistance, would that make it more likely to be the sockets?

[loudthud]

Does this amp have the 100 ohm resistors to form a virtual center tap connected to the 6V6 cathodes and also have the center tap (green wire with yellow stripe) to the heater winding grounded?

[Jonny toetags]

Does this amp have the 100 ohm resistors to form a virtual center tap connected to the 6V6 cathodes and also have the center tap (green wire with yellow stripe) to the heater winding grounded?

I followed the Mission layout exactly, except my green/yellow is grounded as per Classictone's instructions:

"For our 40-18021 PT, use the two BLKs for the BLK and WHT leads. There is no BLU lead - it's not used on this amp. All of the other colors are the same.
You can ground the GRN/YEL lead providing that none of the GRN leads are grounded AND the pilot lamp socket is NOT grounded. Using Mission's layout, the GRN/YEL lead can be grounded"

[Tom Phillips]

I followed the Mission layout exactly, except my green/yellow is grounded as per Classictone's instructions:

"For our 40-18021 PT, use the two BLKs for the BLK and WHT leads. There is no BLU lead - it's not used on this amp. All of the other colors are the same.
You can ground the GRN/YEL lead providing that none of the GRN leads are grounded AND the pilot lamp socket is NOT grounded. Using Mission's layout, the GRN/YEL lead can be grounded"

I think that's the root of your problem. There are too many cooks tossing ingredients in your 5E3 stew.

1: The Mission circuit is not stock. It utilizes a DC lift on the heater circuit via the two 100 Ohm resistors connected from the heater wires to the + side of the cathode bypass capacitor.

2: The Classictone instructions assume that you are not using a heater DC lift circuit. In that case it would be proper to ground the Grn/Yel lead which is the center tap of the heater winding.

Conclusion: You can do #1 or #2 but NOT BOTH. My recommendation is that you disconnect the Grn/Yel wire from ground. Just insulate the end and stow it neatly in the wire bundle. I think that will solve your problem.

Please try that and report back. It's interesting that the amp sounded good as reported in your first post. I venture to say that it wouldn't have sounded good for long. Were the tube plates glowing red?

Cheers,
Tom

Edit: When I quickly checked back I didn't notice the other replies. I see that loudthud was on to this too as was Jazz P Bass. But it's confusing that you said you measured the 50 Ohms with the wire from the 6V6s to the parts board lifted. Did you mean mesured at the tube socket pin or at the eyelet? These details are important. Your next report will tell us more I'm sure.

[loudthud]

Yep, that's it. Too many cooks. Note that 250 ohms in parallel with 50 ohms is 41.6 ohms.

[Jonny toetags]

Just got in from work and haven't really sat down with the amp yet, but i checked pin 8 again (at socket)...had 50 ohms on it.
I unscrewed the ground lug and I'm reading infinite now.
Looks promising!

[Jonny toetags]

Alrighty...here's what I'm running:

5Y3 pin2/8=389.3 Vdc
6V6 pin3= 377 vdc on one, 375 vdc on the other
pin4= 334.4 vdc
pin8= 20.4 vdc
preamps pin 1= 156.2 vdc on one and 144.6 on the other
bias reading on my meter is 37.75 mA

the ONLY thing i notice now is a slight white background noise, which stays the same between vol at 0 and at 10. Not the end of the world, but it was dead quiet before. When i touch the chassis, i can here it ever so slightly through the speaker.
Classictone had mentioned that that GRN/YEL could be grounded to reduce noise....but it also caused my major problem. So who knows.

Edit:
Noticed, with the amp on, volumes at 0, if i approach the amp with my hands, there is a humming that gets louder as i move my hands. if i touch the chassis, with one hand, the noise disappears. im guessing grounding issue?

[Tom Phillips]

...Classictone had mentioned that that GRN/YEL could be grounded to reduce noise....but it also caused my major problem. So who knows.

Grounded grn/yel (heater center tap) is ONE way (#2 in my post 25) to reduce noise in the heater circuit. It reduces hum & buzz but not hiss. There is more than one way to reduce the heater circuit noise and your amp is currently set up to do it a different way (#1 in my post 25). You could switch to the #2 method by grounding the grn/yel AND removing the two 100 Ohm resistors connecting each side of the heater circuit to the 6V6 cathodes (pin 8). However, I wouldn't expect that change to make your amp quieter.

Glad you got it working.
Tom

[Jonny toetags]

Grounded grn/yel (heater center tap) is ONE way (#2 in my post 25) to reduce noise in the heater circuit. It reduces hum & buzz but not hiss. There is more than one way to reduce the heater circuit noise and your amp is currently set up to do it a different way (#1 in my post 25). You could switch to the #2 method by grounding the grn/yel AND removing the two 100 Ohm resistors connecting each side of the heater circuit to the 6V6 cathodes (pin 8). However, I wouldn't expect that change to make your amp quieter.

Glad you got it working.
Tom

Thanks for all the help. You guys really came through.
The hiss is way more prominent on the bright channel vol. The other one only hisses only when the level is up near 8-9