5F1 Fender Champ Troubleshoot

[Bonzai_Musik]

Hey there,
So I'm almost finished building a clone of the 5F1 champ and was observing that my plate dissipation was way too high (14W) with 340V on the plate of the 6V6. So I went ahead and added a 10K resistor before the first filter cap. To place it I used the unused pins of the 5Y3 but once I turned the amp back on, my voltage was half of before and kept dropping to very low numbers.
I soldered everything back to the way it was, I think I'll try another way to place the 10K tomorrow.
But do you have any what was the cause of this ? Or any tips on how to fix it ?
Thanks a lot

 

[dmp]

If you are trying to lower the dissipation you could adjust the cathode resistor so it isn't biased so hot

 

[Bonzai_Musik]

Yes I know but the plate voltage was also way too high compared to the max rating so I thought I would start by that.

 

[rock soderstrom]

Yes I know but the plate voltage was also way too high compared to the max rating so I thought I would start by that.

Your 10k resistor is way too big. The entire current of the amplifier flows through this resistor which results in a high voltage drop, check Ohms Law. The better position of the (now smaller) resistor would be after the first capacitor in the path to the primary winding of the OT.

 

[rock soderstrom]

If you are trying to lower the dissipation you could adjust the cathode resistor so it isn't biased so hot

+1

 

[Bonzai_Musik]

Your 10k resistor is way too big. The entire current of the amplifier flows through this resistor which results in a high voltage drop, check Ohms Law. The better position of the (now smaller) resistor would be after the first capacitor in the path to the primary winding of the OT.

Well I added 10k because I tried switching the original 10k to a 22k which gave the appropriate voltage except the voltage on the plate of the OTn since the resistor is after that.

 

[rock soderstrom]

Well I added 10k because I tried switching the original 10k to a 22k which gave the appropriate voltage except the voltage on the plate of the OTn since the resistor is after that.

Again Ohms law. You have two paths in which different currents flow after the first capacitor. Path 1 leads to the preamplifier which has a very low current flow and path 2 to the power amplifier which has ten times or more current flow. If you install a resistor before the first capacitor, the whole current of the amplifier will flow over it, at 10k you will have the corresponding (extreme) voltage drop. This is a completely different situation than if you only double the series resistor into the preamplifier, since the output stage is also affected.

 

[dmp]

There's a ton of 6v6 amps with higher plate voltages. Princeton reverb has 410 on the plates!

Read this thread
https://el34world.com/Forum/index.php?topic=16193.0

 

[Bonzai_Musik]

Again Ohms law. You have two paths in which different currents flow after the first capacitor. Path 1 leads to the preamplifier which has a very low current flow and path 2 to the power amplifier which has ten times or more current flow. If you install a resistor before the first capacitor, the whole current of the amplifier will flow over it, at 10k you will have the corresponding (extreme) voltage drop. This is a completely different situation than if you only double the series resistor into the preamplifier, since the output stage is also affected.

Yep you are very right on this ^^', I put just a 120 R before the filter caps and got the right voltages (regarding the schematic).
I know I could let it with higher plate voltage and plate dissipation but I'd like to keep my tube alive as long as it can. x)

 

[abbey road d enfer]

But do you have any what was the cause of this ?

I would surmise you use a power transformer that's designed for vacuum tube (valve) rectification and you use silicon rectifiers. The latter have much less (actually negligible) voltage drop compared to a valve that drops about 20-40V.

Or any tips on how to fix it ?

I would suggest you install resistors in series with each diode. That's what would emulate best the drop and sag of a vacuum tube rectifier. I would start with two 220 ohms 5W.

 

[AnalogPackrat]

I would surmise you use a power transformer that's designed for vacuum tube (valve) rectification and you use silicon rectifiers. The latter have much less (actually negligible) voltage drop compared to a valve that drops about 20-40V.

He mentions that he's using a 5Y3 in his first post.

 

[Mworthin]

Hey there,
So I'm almost finished building a clone of the 5F1 champ and was observing that my plate dissipation was way too high (14W) with 340V on the plate of the 6V6. So I went ahead and added a 10K resistor before the first filter cap. To place it I used the unused pins of the 5Y3 but once I turned the amp back on, my voltage was half of before and kept dropping to very low numbers.
I soldered everything back to the way it was, I think I'll try another way to place the 10K tomorrow.
But do you have any what was the cause of this ? Or any tips on how to fix it ?
Thanks a lot

Was this a Sovtek 5Y3? At least some of them have less voltage drop than other 5Y3 rectifiers (see High voltage from Sovtek 5Y3GT - 18Watt.com). I got one of those Sovteks after my NOS rectifier died, didn’t like the plate voltages I was getting and made the transition to a Weber Copper cap rectifier in my 5F2A clone.