Design using EL42 output pentodes - Page 6

Eli Duttman · 12th September 2008, 12:01 AM

Quote:

I'm having trouble finding the 10M45S's in the UK though, does anyone have a couple spare they would be willing to sell?

The 10M45S is the simplest CCS load, but plenty of decent designs are available. IIRC, forum member "Pinkmouse" is a UK resident. Perhaps he or another UK resident member will part with a pair of CCS PCBs that were group ordered, some time ago. Those boards should be populated with "P" type BJTs, for this job.

Merlinb · 20th September 2008, 04:07 PM

Quote:

Originally posted by phil_2
Hi all, not had much to say for a while because I've been busy collecting parts for this project... I'm having trouble finding the 10M45S's in the UK though, does anyone have a couple spare they would be willing to sell? please?

BTW thanks for the advice on possible stability issues, my copy of 'building valve amplifiers' is in the post, I will be reading up on these issues and although I hope it won't be necessary, I do have access to a 'scope at work if needed

Phil.

How are you getting on with this Phil? I think you may be able to use any old voltage regulator for the CCS. A 7812 with 4.7k set resistor would be worth a shot.
Aslo, youmay need to add pole slugging caps in parallel with the power valve's grid leak resistors to maximise stability. I'm thinking 47pF will be in the right area.

Alastair E · 20th September 2008, 05:15 PM

I think George, (Tubelab) has some of those CCS chips around, Maybe worth sending him a email. Not sure where he gets them, but I know he uses them as part of the Power-drive scheme....

phil_2 · 20th September 2008, 09:49 PM

Thanks for the heads up guys

I've actually bought some CCS kits using the 10M45Ss off ebay now to keep the project moving. I'm also waiting for a whole bunch of other parts to arrive before I can start building, I'm keen to get started

I will try the caps as you suggest Merlinb and I'll keep this thread updated as things progress.

phil_2 · 17th October 2008, 08:51 AM

Hi Guys, sorry its been a while, don't think that I've given up or anything, not for a minute! My output transformers have finally arrived and so have the other parts. In the mean time I have read 'Building Valve Amplifiers' which I purchased first, and I'm well into 'Valve amplifiers' which I bought second as I realised while reading 'BVA' that I needed it! Great books both of them. I've also been reading heaps of threads on this forum.

I have planned out my chassis and should be cutting the sheet aluminium on the weekend, all being well.

One question while I'm planning out switch locations etc, Is it worth including a triode/UL switch? will the amp work in UL mode? or is it likely to be unstable? I notice the output transformers have 40% taps...

Thanks again for all your help so far.

Phil.

phil_2 · 25th October 2008, 11:12 AM

Hello again, I just wanted to post a few pictures just to show that progress is being made

Obviously it now needs wiring up and also I'm yet to make a wooden frame for it yet. I'm pleased with how its coming together, hope you like it too. more pics to follow as things progress, which shouldn't be very long.

Phil.

phil_2 · 29th October 2008, 06:35 PM

Hi guys.

I need some help please...Eli!? I have wired one channel and checked my wiring before powering up. I can hear music VERY faintly on the output, other symptoms are that R9, the 18.2k metal film resistor gets very hot and smells (it hasn't burnt out yet tho as I haven't run it for long) and the CCS, when measureing across the 100 Ohm resistor I get 2.2V = 2.2mA no matter where the pot is set? any ideas what the cause of these problems is? are there any other measurements I can take to help identify the problem?

thanks. phil.

phil_2 · 30th October 2008, 06:21 PM

I've heard mention of setting/testing CCS's independantly (I think it was Tubelab?) by connecting them across a 9v battery, is it safe to do this with the 10M45S with no other load than the 100 Ohm resistor?

Also, regarding the cathode resistor R9 mentioned above, could it just be that the resistor isn't up to the power rating required? I've used a 0.75W resistor here.

Thanks. Phil.

phil_2 · 30th October 2008, 08:26 PM

I've got music!!!

I had the CCS wired wrong... in my defence the kit bought off ebay had two holes marked 'A' its quite confusing...

The cathode resistor for the phase splitter now runs cool aswell, so it looks like both problems are solved.

I can't really vouch for soung quality yet, I've only used a small test speaker so far. I'll wire the other channel and let you know.

phil_2 · 12th November 2008, 12:43 PM

Just a bit of an update, and feedback for those who helped me with this.

Both channels are now built and I've spent a bit of time listening to the amplifier. Baring in mind that none of my equipment could be called Hi-end and my speakers are actually small bookshelf speakers with 85db efficiency, with a bad low frequency response... the sound is good, very nice

I was worried about the concerns expressed about low end frequency response and potential stability issues. firstly the amp is stable and produces sufficient power for my small (very small) listening room.

Secondly, bypassing the 12nf input caps shows little noticeable improvement in bass response (only just about noticeable in deep dub style reggae bass lines) probably because of my speakers inability to play the really deep stuff anyway. Bypassing them did however noticeably increase distortion at higher volume levels so I've left them in. Limiting the low end bandwidth was a worthwhile compromise in this case.

So to conclude I would like to do something I've been waiting to do, but couldn’t until I had a working amplifier; and say a BIG thank you to those who helped me out here, especially Eli. Its been a really fun project

When I finally get my cheap circular saw to behave and cut the right angles, or give up and pay someone to cut them for me... I will be able to finish off the wooden base and post a pic of the finished amplifier.

Phil.

20th September 2008, 05:15 PM	#53
Alastair E diyAudio Member Join Date: Feb 2004 Location: South Wales	10M45's I think George, (Tubelab) has some of those CCS chips around, Maybe worth sending him a email. Not sure where he gets them, but I know he uses them as part of the Power-drive scheme.... __________________ Das Beste Oder Nichts

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20th September 2008, 09:49 PM	#54
phil_2 diyAudio Member Join Date: Jul 2008	Thanks for the heads up guys I've actually bought some CCS kits using the 10M45Ss off ebay now to keep the project moving. I'm also waiting for a whole bunch of other parts to arrive before I can start building, I'm keen to get started I will try the caps as you suggest Merlinb and I'll keep this thread updated as things progress.

17th October 2008, 08:51 AM	#55
phil_2 diyAudio Member Join Date: Jul 2008	Hi Guys, sorry its been a while, don't think that I've given up or anything, not for a minute! My output transformers have finally arrived and so have the other parts. In the mean time I have read 'Building Valve Amplifiers' which I purchased first, and I'm well into 'Valve amplifiers' which I bought second as I realised while reading 'BVA' that I needed it! Great books both of them. I've also been reading heaps of threads on this forum. I have planned out my chassis and should be cutting the sheet aluminium on the weekend, all being well. One question while I'm planning out switch locations etc, Is it worth including a triode/UL switch? will the amp work in UL mode? or is it likely to be unstable? I notice the output transformers have 40% taps... Thanks again for all your help so far. Phil.

25th October 2008, 11:12 AM	#56
phil_2 diyAudio Member Join Date: Jul 2008	Hello again, I just wanted to post a few pictures just to show that progress is being made Obviously it now needs wiring up and also I'm yet to make a wooden frame for it yet. I'm pleased with how its coming together, hope you like it too. more pics to follow as things progress, which shouldn't be very long. Phil.

29th October 2008, 06:35 PM	#57
phil_2 diyAudio Member Join Date: Jul 2008	Hi guys. I need some help please...Eli!? I have wired one channel and checked my wiring before powering up. I can hear music VERY faintly on the output, other symptoms are that R9, the 18.2k metal film resistor gets very hot and smells (it hasn't burnt out yet tho as I haven't run it for long) and the CCS, when measureing across the 100 Ohm resistor I get 2.2V = 2.2mA no matter where the pot is set? any ideas what the cause of these problems is? are there any other measurements I can take to help identify the problem? thanks. phil.

30th October 2008, 06:21 PM	#58
phil_2 diyAudio Member Join Date: Jul 2008	I've heard mention of setting/testing CCS's independantly (I think it was Tubelab?) by connecting them across a 9v battery, is it safe to do this with the 10M45S with no other load than the 100 Ohm resistor? Also, regarding the cathode resistor R9 mentioned above, could it just be that the resistor isn't up to the power rating required? I've used a 0.75W resistor here. Thanks. Phil.

30th October 2008, 08:26 PM	#59
phil_2 diyAudio Member Join Date: Jul 2008	I've got music!!! I had the CCS wired wrong... in my defence the kit bought off ebay had two holes marked 'A' its quite confusing... The cathode resistor for the phase splitter now runs cool aswell, so it looks like both problems are solved. I can't really vouch for soung quality yet, I've only used a small test speaker so far. I'll wire the other channel and let you know.

12th November 2008, 12:43 PM	#60
phil_2 diyAudio Member Join Date: Jul 2008	Just a bit of an update, and feedback for those who helped me with this. Both channels are now built and I've spent a bit of time listening to the amplifier. Baring in mind that none of my equipment could be called Hi-end and my speakers are actually small bookshelf speakers with 85db efficiency, with a bad low frequency response... the sound is good, very nice I was worried about the concerns expressed about low end frequency response and potential stability issues. firstly the amp is stable and produces sufficient power for my small (very small) listening room. Secondly, bypassing the 12nf input caps shows little noticeable improvement in bass response (only just about noticeable in deep dub style reggae bass lines) probably because of my speakers inability to play the really deep stuff anyway. Bypassing them did however noticeably increase distortion at higher volume levels so I've left them in. Limiting the low end bandwidth was a worthwhile compromise in this case. So to conclude I would like to do something I've been waiting to do, but couldn’t until I had a working amplifier; and say a BIG thank you to those who helped me out here, especially Eli. Its been a really fun project When I finally get my cheap circular saw to behave and cut the right angles, or give up and pay someone to cut them for me... I will be able to finish off the wooden base and post a pic of the finished amplifier. Phil.