Steptoes amp.

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Alex Kitic
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#106

Post by Alex Kitic »

Mike H wrote: For the low current one, maybe it's cathode has been stripped?
I wouldn't know: if that's the case, it didn't happen in this amp.
I don't think there is a cure for that...
Paul Barker wrote: There is a grey background in the results block, now. Thanks whoever improved it?
Wasn't me... but there should be a cure for that, I hope...
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Paul Barker
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#107

Post by Paul Barker »

It's Ok I liked it, to differentiate it. So I have fiddled with the look a little now.

I have kept one which doesn't have public access to recover from if someone accidentally messes it up.
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Paul Barker
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#108

Post by Paul Barker »

Mike H wrote:For the low current one, maybe it's cathode has been stripped?
I agree. It was a long time ago when I bought all my 813's second hand off eBay. A large percentage wer plain worn out, even though they looked like new. I did make plenty of noise about it at the time. Just as I made plenty of noise about the condition 212's get into. In the case of 212's it was a much more painful problem to the finances. I think my average price was £250 for used ones, and when you devide it up by the ones which transpired to be old cripples the cost to me for each one I now own that works at all must be £500.

It is a strange thing about the interweb that people write all these wanderful websites with great graphics great write up on their circuit and ulogies about their wonderful amp but nobody else seems to mention all these pitfalls.

The 211's I own have done me a much greater service, the GM70's are bullet proof, and I have no doubt the GK71 likewise, because we know that those are genuin NOS, only because of the huge amount of surplus from the Russian sector, there is no value attached so not worth touting worn out ex transmitting valves on the second hand market.

the problem with the 212's is the man looking for them is like a man looking for hens teeth. the listing only ever says there is filament continuity but can't test the valve. You only need one other bidder as keen as mustard and the two of you have made yourself pay silly money for a wore out ex transmitting valve which was removed due to it no longer being effective.

Oh to go back with this head on those shoulders.

Was it worth it? No. But i am older stronger and wiser through the experience.
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Steptoe
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#109 Steptoe's amp

Post by Steptoe »

Dear Pre 65, I must apologise for getting off the subject of Steptoe's amp on this forum. I certainly haven't lost interest in it and hope you haven't either. It is just that I am still wittering on about my GPO transformers, which I am hoping to modify for use in it if the inductance can be brought up to scratch, particularly now I know that the increase in weight need not be fatal.
Thanks to Paul and Alex I have finally sussed out how to measure the inductance so it should be all systems go from now on.
Although I was aware that the little grey cells had deteriorated I hadn't realised how far the process had gone and it looks like it's time to abandon the habits of a lifetime and buy a calculator.
My final question,at least for today, is whether there are any preferred values for the two caps? I have no idea what the inductance is but it's probably low.
Once again, many thanks for your indulgence. Best wishes Steptoe.
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Mike H
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#110

Post by Mike H »

Phil showed me the insides of one of those GPO trannies, well made, core not too small BUT is not gapped so won't work in any single-ended application.

And can't be made to UNLESS you can pull the laminations apart and reassemble them with a gap.

HTH
 
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Paul Barker
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#111 Re: Steptoe's amp

Post by Paul Barker »

Steptoe wrote: My final question,at least for today, is whether there are any preferred values for the two caps? I have no idea what the inductance is but it's probably low.
Once again, many thanks for your indulgence. Best wishes Steptoe.
If you have electrolytics lying around 47uF each would do. If you only have those gpo oil caps parlell them up to get close to those values. But not a huge issue. Aslong as you know the value of the second cap you will find the value of the transformer.
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Paul Barker
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#112

Post by Paul Barker »

Mike H wrote:Phil showed me the insides of one of those GPO trannies, well made, core not too small BUT is not gapped so won't work in any single-ended application.

And can't be made to UNLESS you can pull the laminations apart and reassemble them with a gap.

HTH
I recommend parafeed, as mentioned earlier. You have suitable caps Steptoe you just need some chokes.
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Mike H
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#113

Post by Mike H »

Ah right yes.
 
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Alex Kitic
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#114

Post by Alex Kitic »

1) What exactly are those GPO transformers? I am missing that part.

2) If the transfrormers are not gapped, the simple option would be to find or acquire one choke per channel. At 60mA current draw, even a small choke might be made with nice inductance(25 to 30H).

3) I really do not understand why the output tubes are going to be used in triode mode, when it is easy to use them in pentode mode, with RH style feedback. Beside more output power, the output resistance would be lower in RH mode, all playing towards use with smaller and cheaper output transformers/chokes.

4) If the problem for the above is the chosen driver triode, I can quickly prepare some model to optimize the anode and feedback resistors. Anyway, that tube is quite similar to ECC82/6SN7, thus an application similar to the RH Universal ver2 is readily available...

I would really like to help...
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Mike H
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#115

Post by Mike H »

Alex Kitic wrote:1) What exactly are those GPO transformers?
Good question! :wink:
 
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#116 steptoe's amp

Post by Steptoe »

Dear all, thanks for your continued assistance, which is all the more appreciated as I know this is not really your main interest. Mike, reluctant as I am to question your observations, I have been up real close and personal to these transformers. having pulled some apart and I think they do have a gap in the core. It is not,however, like a normal choke where the E laminations are all the same and are covered by a sort of bar, leaving a gap all along the top. In these, all laminations are E type, but with unequal legs so when joined together there is a gap between the ends of the legs which alternates on each side.But that's not all. Each winding consists of a pair of wires in parallel and is wound from the middle of the wire round the core in opposite directions, with half of one winding being wound on top of half another one. There are 4 identical windings like that, resulting in a very complicated arrangement and the one i describe is the simplest type. The core is nickel iron and they have an iron case.
A considerable amount of effort has gone in to making them so I think they must be useful for something.
In answer to your and Alex's question, some years ago everyone was replacing their old electro mechanical exchanges with new ones and lots of people asked if I would take out the old gear if they let me keep it.
Of course there was never any doubt about my answer so I now have a fair sized mountain of them. More recently my kids have made it very clear that they don't want to be left with that particular legacy so I've started thinking about recycling them, so here I am.
They contain three types of transformer similar to the one described above, together with wire wound resistors, grease filled capacitors and millions of relays and I have to find a use for all of them before I die.
If you have any ideas I'd be delighted to hear them and if it would help to examine any of this stuff I will send it to you. With best wishes, Steptoe.
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Paul Barker
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#117

Post by Paul Barker »

That lamination arrangement has a special name. I think it is called L E . The E's are longer than usual so that they go right past the end of the bobbin and out equidistant to the other end. Then you put the next E back to front with this one and so on. So what you see is a gap at each end, but with no I to fill it.

They can't take much DC current though, you would be best to treat them as parafeed transformers.

I would be delighted to test them for you.
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Alex Kitic
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#118 Re: steptoe's amp

Post by Alex Kitic »

Steptoe wrote:Each winding consists of a pair of wires in parallel and is wound from the middle of the wire round the core in opposite directions, with half of one winding being wound on top of half another one. There are 4 identical windings like that, resulting in a very complicated arrangement and the one i describe is the simplest type. The core is nickel iron and they have an iron case.
A considerable amount of effort has gone in to making them so I think they must be useful for something.
...
If you have any ideas I'd be delighted to hear them and if it would help to examine any of this stuff I will send it to you. With best wishes, Steptoe.
The description clearly shows that these transformers are not suitable for classic SE, but they might be perfectly good for parallel-feed.

All you need are 2 chokes, and these should not be expensive or difficult to source. 20-30H at 50-60mA should suffice.

The bifilar nature of the winding seems to indicate another possible use, as push-pull. While we are very much taken with SE, PP is very worthwhile, and if the problem might be DC balance (avoiding any imbalance because the core is Nickel-Iron), this is easy to solve using LM317 CCS under each tube in PP mode. Of course, the output stage can be operated exclusively in class A, but I have the impression that output power is not the most important part of the equation.
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Mike H
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#119

Post by Mike H »

Steptoe wrote:I am to question your observations, I have been up real close and personal to these transformers. having pulled some apart and I think they do have a gap in the core. It is not,however, like a normal choke where the E laminations are all the same and are covered by a sort of bar, leaving a gap all along the top. In these, all laminations are E type, but with unequal legs so when joined together there is a gap between the ends of the legs which alternates on each side.
Paul Barker wrote:That lamination arrangement has a special name. I think it is called L E . The E's are longer than usual so that they go right past the end of the bobbin and out equidistant to the other end. Then you put the next E back to front with this one and so on. So what you see is a gap at each end, but with no I to fill it.

They can't take much DC current though, you would be best to treat them as parafeed transformers.

I would be delighted to test them for you.
I have seen the core. Yes the lams are all 'E's and the legs are different lengths, and they alternate so that the legs overlap those below and above. Still no gap though, all that separates the lams is the usual thin varnish that you normally get on any lams in any transformer. Any 'gap' at the edges of the ends of the legs doesn't count, because of the magnetic circuit that exists through the overlaps, them being packed together.

Hope that makes sense. Must be said though it's a neat looking belt and braces method of building a non-gapped core.
 
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#120 steptoes amp

Post by Steptoe »

Dear Mike,further to your comments I have had another look at these transformers and as I find it difficult to explain the construction in words I wonder if I could send you one or more to look at? Paul has also kindly agreed to test them to see if they're any use so if either, or both of you can tell me how to get them to you I'll have them parcelled up asap. With best wishes, Steptoe.

PS. Since starting this project I've been trying to figure out what the aether is made of, without success, so if anyone can enlighten me I would be most grateful. As far as I can work out it is something with no mass unless it is moving so when at rest it would seem not to exist at all, a concept which I just can't get my head around.
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