6100 LE / EL 34 Capacitors

[Spanngitter]

The hum is there on standby , and it is coming through the speakers

Nothing unusal, this is magnetic interference between the Power Transformer and the Output Transformer. Sometimes it helps to tighten up the mounting bolts to ensure the frame of the transformer has good ground / connection to chassis, but to resolve it ultimatively, it would require a Mµ Metal shield placed over the PT or OT to block any magnetic radiation.

 

[Thoma]

... I saw a shopping list here from Mouser , but I can not find it now. Can anyone point me in the right direction ? ...

Perhaps you have seen this before

 

[Thoma]

Co

I had one on the bench 20+ years ago.

Could tell by your response.😉

All my four 30th Anniversary Series Amps have just a very little hum while on standby, As soon as standby is switched off, hum goes to close to zero.
Recently I had the pleasure to test six gold/blue 6100LEs side by side. All showed the same effect, that is only noticeable in a perfectly quiet room anyway.

I doubt that there's anything to worry about, if the hum is close to unnoticeable. But if we're in doubt I'd have a good amp technician look into it.

 

[Sixs]

She been acting up again . Long story -working on and off . opened her up , nice and clean , cant see any "hot spots", dosen't smell burnt. The caps still have the right shape. That must be Good . One of the JJ EL34 was missing the guide pin. Don't want to mess with them. Tomorrow - clean pots /sockets, replace all 4 PT ,bias and see how it goes.

 

[Dirty-D]

Filter caps? they're a value of 50/50/50mfd at like 500 volts l think.it's ARS marked on the body if l remember.Changing those evey 10-15 years can bring the amp back to life. I'm just talking like we're in the bathroom at a club though. Confirm this with a real tech

 

[Mike_LA]

On and off how?
Won't start
cuts out?

 

[Trouble]

Filter caps? they're a value of 50/50/50mfd at like 500 volts l think.

There is no 50 uf caps in this amp, you must be thinking of another model.

 

[Sixs]

On and off how?
Won't start
cuts out?

It's very hard to pin point. It been an intermittent problem . I've been testing in all configurations - High - Low (100-50w) , pentode or Triode : this dosen't seem to matter much. Sometimes the sound has been low and weak or totally gone. But It can jump back to full strength in the middle of a chord .
However after I have changed the EL 34's with a new mached set , It has been smooth all the time. - in all power modes. Channel 1 is quiet ,while 2 and 3 have some noise. Makes me belive one or more of the pre amp tubes needs is doing this - I've been rolling pre amp tubes - so maybe not so strange (out of a box of used ones).
One thing that puzzles me now ,is that my EuroTubes Bias probe is having a hard time reading the values - they are jumping all over the place , but usually end up with a plate voltage - 0.0 vdc after about a 1 min. But the guitar still sings , without a hitch.
I tested the Bias probe on another amp , and it works flawless. I don't want to run the 6100 for too long before I find out whats going on,
I'm working on it - Update will follow

 

[Thoma]

I'd look at the many connectors inside the amp and tap them with an isolated stick. Particularly the ones with shielded cables can cause issues if there's oxidation on contacts. The same is true for all the little switches and all pots. If your bias probe gives you erratic readings, this might be issues due to contact resistance in tube sockets.

In one case I had a dirty PT socked in one of my blue heads.

I used a mild tuner spray for cleaning.
Be careful with contact cleaner sprays. Some contain acids that cause corrosion.
There are cleaner sprays for washing/relubrication after using aggressive contact sprays.

Good luck!

 

[Sixs]

I'd look at the many connectors inside the amp and tap them with an isolated stick. Particularly the ones with shielded cables can cause issues if there's oxidation on contacts. The same is true for all the little switches and all pots. If your bias probe gives you erratic readings, this might be issues due to contact resistance in tube sockets.

In one case I had a dirty PT socked in one of my blue heads.

I used a mild tuner spray for cleaning.
Be careful with contact cleaner sprays. Some contain acids that cause corrosion.
There are cleaner sprays for washing/relubrication after using aggressive contact sprays.

Good luck!

Will do ! I did do a good cleaning of all the pots and push buttons and sockets . That pretty much took care of the scratching they were making. I'll poke around with wire/connections tomorrow.
I've been measuring on V8 and V9 . i might have been a little unclear in my last post ,but after the tube change, I get a steady reading of the Ma. ,but no plate VDC. I'm getting 50.0 ma in 100w mode and 48,5 ma in 50w on both sockets . Flicking the stby to on , plate current reads a (normal) Vdc , but drops right down to 0.0 Vdc, very fast( seconds). Does not help wiggeling the probe socket- steady at 0.0 VDC .Guitar plugged in - still plays loud and clear . How can that be ?? The Bias probe is linked in series between the tube and socket. Tested the Bias probe on a laney LC 50 , 6L6 tubes (great amp) and i get rock steady readings of both ma and plate voltage.

 

[Sixs]

Since I can't bleed the caps direct on the 6100 , is grounding pin nr 3 , via a resistor , on all 4 el34 sockets the correct procedure ? Thanks !

 

[PelliX]

You wouldn't need to do it on each socket, but what exactly is the issue with bleeding the caps?

 

[Sixs]

Thanks ! Safety . Got to know how to make my amp safe my to work on. I'm going to poke around a little, with my plastic chop stick.

 

[Sixs]

To measure plate volts - Fluke /VDC on pin 3 , with Tubes in ? Just ask'n ?

 

[Mike_LA]

Seems like you have a meter, you can bleed the caps thru your meter and watch the voltage drop.
Someone correct me if I am wrong but I believe set on DC voltage.
One side to ground and set your meter to high voltage and see what you are doing . . . . . .

 

[Sixs]

Thanks. . I did use the meter first . There was nothing there , The power cord has been out a few days /stby off. I measured the four 1k resistors (r251-254) . Now i'd like to measure the plate voltage , since I'm getting 0.0 VDC on my bias probe -and I don't think that can be right . And then Bias. I'd like confirmation that it is measured on pin 3 , VDC , with speaker load

 

[Mike_LA]

Bias info

 

[Sixs]

I here is what I have on pin 3 measured with the Fluke multimeter. 16 ohm speaker load. Only measured on V8 and V9
V8 = 443 VDC
V9 = 446 VDC
Adjusted Bias to 38,5 ma / 25w tubes.

ON STANDBY , there is a plate voltage of 75 VDC on both V8 and V9. Is this correct ? If not, what could cause this ? Bad stby switch ? Help Needed !

Other Finds: one of the 1k resistors (R 253) was 1,4 k

Found the fault on the Euro tubes Bias probe. The Plate voltage LCD screen needed a little "presure"/push against it's chassis - it has a pin connector inside.

 

[Sixs]

Put everything back together , and it has worked without a hiccup for 2 days. Even the static noise on ch 2 , which came after some tube rolling, is gone .
So I guess order is restored again and - well ,it's way better now. May it last !
If I have have got it right, 70Vdc on the plate in standby (pin 3), is normal.
Thanks for the help and advice so far. Time to hunt down the caps and some resistors.

 

[Trouble]

If I have have got it right, 70Vdc on the plate in standby (pin 3), is normal.

Yes that is normal for these amps in standby.