KEL34 just acquired

[goonybird]

Have just acquired a KEL34 in need of some work.
I have located a copy of the circuit diagram but could do with a copy of the actual contruction manual. Any help appreciated.

other points cropping up are:
Mains Tx relocate to top? I just think cosmetically looks more balanced.
and what to do with XLR speaker sockets? Leave or change to binding posts?
Instinct would be change but keeping XLR retains originality

many thanks.

[Greg.]

Hello Goonybird,

I may be able to help you, but first, you would do well to introduce yourself in the Coffee Bar room. Tell us a bit about you, your hi-fi journey and why you have now arrived with a KeL34. Such a step will satisfy the forum requirements and assuming what you say fits, I should be able to release some information to help you.

PS. I don’t make the rules.

[bob orbell]

Yes I agree with Greg, this is a very friendly forum with lots of helpful members, it has a few plonkers as well,. BOB

[Greg.]

Thanks for your introduction, Goonybird and welcome.

If you PM me your email, I should be able to help you with the documents you are looking for.

[goonybird]

Ah Thanks for help. Have decided to keep XLR as found some old metal bodied RS ones in the garage so will make up XLR to Banana socket cables. Got some New 6AU6 and EL34s from Luton Radio Rally to get it going (had some ECC82s lurking)

[Richard]

Originally Posted by goonybird

Have just acquired a KEL34 in need of some work.
I have located a copy of the circuit diagram but could do with a copy of the actual contruction manual. Any help appreciated.

other points cropping up are:
Mains Tx relocate to top? I just think cosmetically looks more balanced.
and what to do with XLR speaker sockets? Leave or change to binding posts?
Instinct would be change but keeping XLR retains originality

many thanks.

Hi Goonybird, sorry for delayed reply, been away. Hope you have the build info you need now if not please pm Matthew or any of the mods.
I had this amp and the follow up Kit88 using a similar mains torroid fitted inside the case. There may be an increase of heat and a visual imbalance but I left them inside and had no problems. Some members moved the mains TX to the top plate and maybe they will tell of any improvement or problems doing this.
I agree with your thoughts about keeping the XLRs for originality. WAD used them as there was a move (EC?) towards safety and 4mm post were being frowned upon for being non shrouded but common sense of the low voltages involved seems to have prevailed. In the end I changed mine to 4mm binding posts as I found the XLRs a pain when swapping gear and testing the amp etc. I carefully fitted blanking plates with screws and drilled them for binding posts and they looked neat.

[goonybird]

Hi thanks for info supplied. Now to get cracking on it.
Will have to post piccies...

It seems like an attempt to convert an integrated Kel34 into just power amp as all phono inputs bar 1 are disconnected as is selector switch. Personally I would use 1 phono pair to bypass as Power Amp in.

Other pointy is I could only pick up odd EL34s NOS from Radio Rally. Not sure if Bias will get upset if I use non matching valves, just for testing to get it up and running.

As before will make up XLR to Banana inline sockets. The actual contact area on XLR pins looks up to the job.

[Richard]

It seems like an attempt to convert an integrated Kel34 into just power amp as all phono inputs bar 1 are disconnected as is selector switch. Personally I would use 1 phono pair to bypass as Power Amp in.


If you want a direct input, disconnect the existing pot to pcb input, or go through the pot as a line input with vol control. If you bypass the existing arrangement without disconnecting it the ground leg of the pot and/or any connected devices will appear in parallel and load down the input.


Other pointy is I could only pick up odd EL34s NOS from Radio Rally. Not sure if Bias will get upset if I use non matching valves, just for testing to get it up and running.


Should be ok if the valves are good and similar match. The amp has some fixed bias -10V pin 5 and some cathode bias +9V pin 8 so check for a similar 9V from pin 8 to ground on each valve and keep an eye for any running away

[goonybird]

Hi thanks. Is it possible to convert to variable bias so it can be set, as on say Radford STA25?

Piccies before anything done, looks like an alps pot.

[Richard]

Originally Posted by goonybird

Hi thanks. Is it possible to convert to variable bias so it can be set, as on say Radford STA25?

Hi, yes but a fair bit of work involved as you'd need 4 pots in place of the R3/R5 bias divider and to include sockets to probe for voltage during adjustment.

Disconnect the 330k gridleaks at point E on the pcb and feed them each from a pot. Then change the cathode Rs for 47R or similar and twiddle away looking for around 20V total bias.

It looks like a single 50k lin pot was used during development at R3/R5. It ended up with half the bias being supplied from the fixed supply and half being developed over the 180R cathode resistors. This meant less power was wasted in the cathode resistors than full cathode bias whilst still allowing enough "automatic" bias between a pair so the fixed amount didn't need adjusting.

The STA25 uses 39R cathode resistors so a couple of volts will be developed there but the pots would need adjusting for the majority.

The Kel34 set up works very well though you'll be pleased to hear(!) given reasonably matched pairs of valves. I can test yours for you if you want to hopefully put them into pairs, pm me, or get a matched quad, Svetlanas were my favourite.