Bob Stuurman EL34 Stereo Amp - UK Vintage Radio Repair and Restoration Discussion Forum

cathoderay57 · 29th May 2020, 12:58 pm

A few years ago I was gifted a home-constructed stereo valve amplifier using 2 pairs of EL34. The circuit and construction article was published in Elektor Electronics magazine in April & May 2003 entitled "Valve Final Amp - 35 watts from a no-frills design. Design by Bob Stuurman". It features Lundahl LL1620/P-P output transformers and a toroidal mains transformer. It works extremely well now, but when I got it, the triode-connected EF86s and the ECC83s were OK but some of the pins on the PCB-mounted octal EL34 sockets had come adrift from the PCB tracks caused by pulling valves in and out. That was easily fixed. It is housed in a recycled TEAC CD player box as you can see from the pic. This is 8cm deep and so accommodates all of the transformers below decks. The enclosure is fit for purpose, but not particularly pretty. The original construction article suggests chassis fabrication from sheet aluminium then adding wooden side panels. Has anybody else built or acquired one of these as I would be interested in their enclosure solution? I have looked at some ready-made amplifier boxes but most are too small and expensive. Cheers, Jerry

vinrads · 29th May 2020, 2:57 pm

Hi Jerry I was thinking along the same line ,constructing the amp on a sub chassis ,mounted under a chrome top ,just the valve bases holes cut out ,the chassis needs to be nearer the underside of the top , is that makes sense. Mick.

Aub · 29th May 2020, 3:16 pm

I remember one article, where the EL34s were fed by solid state devices and there was a free PCB stuck to the front of the magazine. I think I've still got it somewhere. Is this that design? I don't recall the small valves though, but I remember the torroidal mains transformer.

Cheers

Aub

Bookman · 29th May 2020, 4:14 pm

Hi Jerry, just to add to that provided by Mick why not just tinker with what you have. Keep the base plate and think of either spraying the existing cover in chrome or perhaps start looking at using a nice piece of hardwood.
Here is how I rearranged my Dynaco amp. May not be H&S compliant but it is my own personal space. Let us know how things pan out.
Joe

cathoderay57 · 29th May 2020, 4:38 pm

Thanks to all for replies. I had been thinking along the same lines as Mick and Joe i.e. fitting a replacement chromed cover plate for the top and front. I presume that I would have to cut holes for the valves and screw fixing holes out of thin gauge sheet steel and then send it off for chrome plating; not sure how much or where to get it done though? For Aub, it sounds like a different article with the semiconductor drivers. The only solid state devices used are in the power supply with 1N4007 diodes for the bias supply, BYW96E diodes for HT and a 200v zener. For this one I think you had to be a member of the Elektor Electronics website and you could then download the PCB artwork or order the ready-made PCBs from Reader Services. I don't think they were giving them away. Nice job on the Dynaco, Joe.

Stevie342000 · 29th May 2020, 8:04 pm

The Hybrid EL34 project with the free pcb that Aub mentions is in ETI circa Dec 91 and Jan 92. I know as I was looking at it earlier this week. It is on my to do list. However I do not have the PCB but was going to fabricate one should I get as far as building it.

The issue I ran into was trying to find 2k8 push pull output transformers that was as far as I got at this point in time. You can download ETI from American Broadcast History website.

Aub · 29th May 2020, 8:24 pm

Found it! Still has PCB attached.

Stevie, would you like it? I can post it FOC.

Cheers

Aub

Stevie342000 · 29th May 2020, 9:23 pm

Quote:

Originally Posted by Aub

Found it! Still has PCB attached.

Stevie, would you like it? I can post it FOC.

Cheers

Aub

Hello Aub yes please send me a PM and I will send you contact details, thanks very much appreciated.

vinrads · 29th May 2020, 9:35 pm

Quote:

Originally Posted by Bookman

Hi Jerry, just to add to that provided by Mick why not just tinker with what you have. Keep the base plate and think of either spraying the existing cover in chrome or perhaps start looking at using a nice piece of hardwood.
Here is how I rearranged my Dynaco amp. May not be H&S compliant but it is my own personal space. Let us know how things pan out.
Joe

Now that look impressive love the chrome and wood . I was thinking along the same lines for my project , just awaiting the transformers. Mick.

cathoderay57 · 29th May 2020, 9:39 pm

Any tips on getting the chroming done?

Stevie342000 · 30th May 2020, 11:24 pm

Other than getting chrome plating done which will be expensive not to mention toxic. It can be cleaned up with Quick Glo Chrome Cleaner - fine only see Blueglow electronics on YouTube not sure which video but it will be under restoration.

A motor body repair shop might be able to help with Chrome plating or they might know where to get it done. Has it not cropped up on The Repair Shop?

Diabolical Artificer · 31st May 2020, 8:11 am

A quick and easy solution would be to screw everything down onto a thick sheet of wood, see pic two for a general idea, if you can find a half decent bit of scrap like Oak or Walnut veneered ply off an old wardrobe, that'd be good. The amp modules just need a bit of a clean or spray paint the metal.

You already have chassis of sorts with the amp modules, rearrange as per pic attached then find a suitable metal box to cover the mains transformer and PSU.

Either drill a couple of holes and fit RCA IP's to the chassis's at the front, or use bent sheet L to make a bracket, same goes for the banana speaker jacks.

Either that or chap over on DIY audio uses boxes from Ikea for a lot of his amps, also things like Ikea T caddys for OPT covers, I'm sure if you wandered round Ikea for half hour you'd find something. See pic 3 and - https://www.diyaudio.com/forums/tube...llery-939.html amp bottom of page. the photo gallery is a good place to look for idea.

Andy.

cathoderay57 · 31st May 2020, 10:51 am

Good ideas, many thanks for the tips and links

tri-comp · 31st May 2020, 12:22 pm

Quote:

Originally Posted by Stevie342000

The Hybrid EL34 project with the free pcb that Aub mentions is in ETI circa Dec 91 and Jan 92. I know as I was looking at it earlier this week. It is on my to do list. However I do not have the PCB but was going to fabricate one should I get as far as building it.

The issue I ran into was trying to find 2k8 push pull output transformers that was as far as I got at this point in time. You can download ETI from American Broadcast History website.

...and the issue you want is 1992, September.

You should also read issue 1992, November, page 10.
The latter deals with errors in the Sept. issue.

Rgds,

/Torben

qualityten · 5th Jun 2020, 9:29 pm

I like the Ikea tea caddy idea for transformer covers!

I've had most success with a sheet of 1.5mm aluminium folded over lengthways, with wooden side cheeks. I'm interested that the TEAC CD player enclosure works for you. It looks neat as is.

David

cathoderay57 · 5th Jun 2020, 9:42 pm

Hi David, thanks for the comments. It certainly sounds very nice at least partlý no doubt to the quality of the Lundahl output transformers that I think are rather expensive. I was very lucky to receive this amp as a gift! Cheers, Jerry

qualityten · 5th Jun 2020, 9:50 pm

The internal work is really neat. I like the almost dual mono construction, and the internal screening of the beautiful, high quality Lundahl transformers.

29th May 2020, 12:58 pm	#1
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Bob Stuurman EL34 Stereo Amp A few years ago I was gifted a home-constructed stereo valve amplifier using 2 pairs of EL34. The circuit and construction article was published in Elektor Electronics magazine in April & May 2003 entitled "Valve Final Amp - 35 watts from a no-frills design. Design by Bob Stuurman". It features Lundahl LL1620/P-P output transformers and a toroidal mains transformer. It works extremely well now, but when I got it, the triode-connected EF86s and the ECC83s were OK but some of the pins on the PCB-mounted octal EL34 sockets had come adrift from the PCB tracks caused by pulling valves in and out. That was easily fixed. It is housed in a recycled TEAC CD player box as you can see from the pic. This is 8cm deep and so accommodates all of the transformers below decks. The enclosure is fit for purpose, but not particularly pretty. The original construction article suggests chassis fabrication from sheet aluminium then adding wooden side panels. Has anybody else built or acquired one of these as I would be interested in their enclosure solution? I have looked at some ready-made amplifier boxes but most are too small and expensive. Cheers, Jerry Attached Thumbnails Last edited by cathoderay57; 29th May 2020 at 1:15 pm. Reason: Add photo

29th May 2020, 2:57 pm	#2
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,762	Re: Bob Stuurman EL34 Stereo Amp Hi Jerry I was thinking along the same line ,constructing the amp on a sub chassis ,mounted under a chrome top ,just the valve bases holes cut out ,the chassis needs to be nearer the underside of the top , is that makes sense. Mick.

29th May 2020, 3:16 pm	#3
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,039	Re: Bob Stuurman EL34 Stereo Amp I remember one article, where the EL34s were fed by solid state devices and there was a free PCB stuck to the front of the magazine. I think I've still got it somewhere. Is this that design? I don't recall the small valves though, but I remember the torroidal mains transformer. Cheers Aub __________________ Life's a long song, but the tune ends too soon for us all.

29th May 2020, 4:14 pm	#4
Bookman Hexode Join Date: Aug 2017 Location: Taunton, Somerset, UK. Posts: 318	Re: Bob Stuurman EL34 Stereo Amp Hi Jerry, just to add to that provided by Mick why not just tinker with what you have. Keep the base plate and think of either spraying the existing cover in chrome or perhaps start looking at using a nice piece of hardwood. Here is how I rearranged my Dynaco amp. May not be H&S compliant but it is my own personal space. Let us know how things pan out. Joe Attached Thumbnails

29th May 2020, 4:38 pm	#5
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Re: Bob Stuurman EL34 Stereo Amp Thanks to all for replies. I had been thinking along the same lines as Mick and Joe i.e. fitting a replacement chromed cover plate for the top and front. I presume that I would have to cut holes for the valves and screw fixing holes out of thin gauge sheet steel and then send it off for chrome plating; not sure how much or where to get it done though? For Aub, it sounds like a different article with the semiconductor drivers. The only solid state devices used are in the power supply with 1N4007 diodes for the bias supply, BYW96E diodes for HT and a 200v zener. For this one I think you had to be a member of the Elektor Electronics website and you could then download the PCB artwork or order the ready-made PCBs from Reader Services. I don't think they were giving them away. Nice job on the Dynaco, Joe.

29th May 2020, 8:04 pm	#6
Stevie342000 Hexode Join Date: Jan 2006 Location: Greater Manchester, UK. Posts: 373	Re: Bob Stuurman EL34 Stereo Amp The Hybrid EL34 project with the free pcb that Aub mentions is in ETI circa Dec 91 and Jan 92. I know as I was looking at it earlier this week. It is on my to do list. However I do not have the PCB but was going to fabricate one should I get as far as building it. The issue I ran into was trying to find 2k8 push pull output transformers that was as far as I got at this point in time. You can download ETI from American Broadcast History website.

29th May 2020, 8:24 pm	#7
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,039	Re: Bob Stuurman EL34 Stereo Amp Found it! Still has PCB attached. Stevie, would you like it? I can post it FOC. Cheers Aub Attached Thumbnails __________________ Life's a long song, but the tune ends too soon for us all.

29th May 2020, 9:39 pm	#10
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Re: Bob Stuurman EL34 Stereo Amp Any tips on getting the chroming done?

30th May 2020, 11:24 pm	#11
Stevie342000 Hexode Join Date: Jan 2006 Location: Greater Manchester, UK. Posts: 373	Re: Bob Stuurman EL34 Stereo Amp Other than getting chrome plating done which will be expensive not to mention toxic. It can be cleaned up with Quick Glo Chrome Cleaner - fine only see Blueglow electronics on YouTube not sure which video but it will be under restoration. A motor body repair shop might be able to help with Chrome plating or they might know where to get it done. Has it not cropped up on The Repair Shop?

31st May 2020, 8:11 am	#12
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,662	Re: Bob Stuurman EL34 Stereo Amp A quick and easy solution would be to screw everything down onto a thick sheet of wood, see pic two for a general idea, if you can find a half decent bit of scrap like Oak or Walnut veneered ply off an old wardrobe, that'd be good. The amp modules just need a bit of a clean or spray paint the metal. You already have chassis of sorts with the amp modules, rearrange as per pic attached then find a suitable metal box to cover the mains transformer and PSU. Either drill a couple of holes and fit RCA IP's to the chassis's at the front, or use bent sheet L to make a bracket, same goes for the banana speaker jacks. Either that or chap over on DIY audio uses boxes from Ikea for a lot of his amps, also things like Ikea T caddys for OPT covers, I'm sure if you wandered round Ikea for half hour you'd find something. See pic 3 and - https://www.diyaudio.com/forums/tube...llery-939.html amp bottom of page. the photo gallery is a good place to look for idea. Andy. Attached Thumbnails __________________ Curiosity hasn't killed this cat...so far.

31st May 2020, 10:51 am	#13
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Re: Bob Stuurman EL34 Stereo Amp Good ideas, many thanks for the tips and links

5th Jun 2020, 9:29 pm	#15
qualityten Octode Join Date: Feb 2009 Location: Wallasey, UK. Posts: 1,312	Re: Bob Stuurman EL34 Stereo Amp I like the Ikea tea caddy idea for transformer covers! I've had most success with a sheet of 1.5mm aluminium folded over lengthways, with wooden side cheeks. I'm interested that the TEAC CD player enclosure works for you. It looks neat as is. David

5th Jun 2020, 9:42 pm	#16
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Re: Bob Stuurman EL34 Stereo Amp Hi David, thanks for the comments. It certainly sounds very nice at least partlý no doubt to the quality of the Lundahl output transformers that I think are rather expensive. I was very lucky to receive this amp as a gift! Cheers, Jerry

5th Jun 2020, 9:50 pm	#17
qualityten Octode Join Date: Feb 2009 Location: Wallasey, UK. Posts: 1,312	Re: Bob Stuurman EL34 Stereo Amp The internal work is really neat. I like the almost dual mono construction, and the internal screening of the beautiful, high quality Lundahl transformers.