Kel34

[Global]

Hi guys

Can anyone point me to a circuit for the original torroid OPT KEL34?

What bias mods were recommended to reduce dissipation?

Finally, bright anode glow from one EL34 which affects any valve in that socket has got to be

1. Loss of fixed bias connection

2. Bad cathode resistor or (more likely) bypass cap.

3. Leaky coupling capacitor.

Have I missed anything?

I have to travel to fix this amp for my son and I want to make sure I take everything I might need!

Thanks

Mark

[petercom]

Originally Posted by Global

Hi guys

Can anyone point me to a circuit for the original torroid OPT KEL34?


Thanks

Mark

Attached is the cct diagram for a start.

[John Caswell]

Hi Mark,
Just dug the cct out.
You will need to take with you,
0.47µF 630V capacitor - coupling cap
180R 7Watt wirewound - cathode bias res
220µF/ 25V elco capacitor - cathode bias cap
330K 1/2 Watt - bias feed resistor.
1k 1/2 Watt - grid stopper
100R 1Watt - g2 feed res
valve base??

That should cover all eventualities. I don't remember any mods to reduce dissipation, but as it is very similar to the Kit/Kat88 you could up the cathode bias res to 220R 7 Watt and also change the negative bias res to give you -12V bias. simplest way to do this is to substitute R3/5 with a 50K pot and adjust for 12Volts

CCt emailed to home ( Now not necessary see Peters email)

John aka Dr John

[Global]

Thanks Peter and John

Will be travelling up to Elgin on 25th with all bits and tools to repair the amp. I tought my son to appreciate the sound but not to do repairs. Oh well, he'll just have to wait for me!

Many thanks again.

Mark

[Global]

Hi

Just thought I would wrap up this thread with the findings.

Turned out to be a shorted coupling capacitor and the lad had hit the 'Off' switch within a second of the hum/plate glow so there was no secondary damage.

Replaced cap and treated the amp to a new quad of EL34s.

Perfect!

THanks for the advice.

Mark

[John Caswell]

Well done!

John aka Dr John