Building a new Leak Stereo 20.

[Westo091946]

Mike
I have dug out the invoice I had four dual Photometers 3 x 2 Meg log/2 Meg log and 1 x 2 Meg log/2 Meg R log the total including postage £42-00. I had to pay a Proforma Invoice. They have quite a range of products available. I have included the e-mail and website info hope this is helpful.

Richard

The company is Blore Edwards Ltd, Unit 25 Aberaman Park Ind Estate,Aberarman, Aberdare RT, CF44 6DA
Sales@blore-ed.com
www.blore-ed.com

[Gabe001]

It seems like you've done your homework and are enjoying yourself with 2 nice projects. Keep us posted with pictures.

If you're using an aluminium chassis remember that if you breathe on it you scratch it, so keep the protective covering on as long as you can.

[Westo091946]

The Transformers from Majestic Transformers are to Leaks Original specifications so no change in characteristics.
The Mullard Amp 5-10 Kit is only Mono, I take your point about the Aluminium chassis and looking to source a steel one.
The most difficult part that I have undertaken so far is the component board not having a workshop so no drill stand all hole drilled by hand with a battery drill, also hand punching the hole through rivets all 64 of them, I am part the way through putting the under component board wiring in. I have a light box and the epoxy board I am using is translucent so I can easily check the finished wiring from the component side will post a picture when it's finished.

My last valve build was a Mullard 3 watt and my first sold state build was the TEXAN amp kit, in it's day it was a fine amp which I used for many years.

The Mullard 10+10 looks an interesting build the only issue is the one impedance 16 ohm output, if I substitute the output transformer with 4-8-16 ohms ratting could anyone tell me what effect could this have on the output stage ?.

[Gabe001]

Drilling a steel chassis with a hand battery drill is going to be very hard. Aluminium is much easier to drill, and even so at the very least to make the bigger holes you'd need an electric drill. Just be careful not to scratch it, that's all.

Also, don't forget to buy a deburring tool.

I don't think 4/8/16 secondaries vs 16 only will make a difference.

[toprepairman]

There is someone making new ST20 chassis copies just like the originals with only a couple of very minor changes.
Google Valvepower Stereo 20 and it comes up.
Also stevesmith350@hotmail.com
No point struggling to drill all those holes.

[Gabe001]

Thanks for that. Very interesting, a replica stereo20 for £1,100. I wonder if the OP's project will work out cheaper

[Westo091946]

It's cheaper than some of the used Leak 20 on eBay not quite sure what the cost is at the moment the most expensive is the Transformers they don't show the component board in there info only that they use turrets on the component board with a pcb.

[toprepairman]

Steve, the man behind the new 20's will be at Tonbridge on the 3rd.

[Westo091946]

Another question, how would you connect UV meters similar to the mackintosh Amp to the Leak 20 for that matter any other valve amp has anybody done this without effecting the performance of the unit.

[barrymagrec]

A standard Bell spec VU meter would need an additional series resistor, value depending on impedance setting to put across the amplifier output.

The impedance of the meter and the low output impedance of the amplifier would mean no loss of quality due to the meter rectifier, however my question would be what purpose would it serve?

[Gabe001]

Originally Posted by Westo091946

Another question, how would you connect UV meters similar to the Mackintosh Amp to the Leak 20 for that matter any other valve amp has anybody done this without effecting the performance of the unit.

Don't do it, they won't look right on a stereo 20 clone.

[Richardgr]

Old PA amplifiers sometimes had an 'overload' or clipping indicator. A circuit like this one might be more in keeping with the Leak 20, and be a useful indicator.

[Gabe001]

When are we going to get some pictures?

[Richardgr]

I was wondering if moving this thread to the Hi-fi and Record Players board might give it a bit more exposure? I stumbled across it when checking for information about tube testers.

[Diabolical Artificer]

I have a lot of experience with fitting "VU" meters to DIY amps. I've always built my VU own meter driver boards but you can get cheap meters & driver board from the usual sources.

However there is a far easier way to do it using the attached circuit with vintage meters. It's just a few resistors and a germanium diode. You may need to alter the value of the 1k dropper, maybe the 390r too with the meters you use.

These won't be true VU meters though, just eye candy, for more info see - https://www.vintage-radio.net/forum/...d.php?t=206266

Lastly I have pairs of vintage meters if you need any. These are WW2 meters but the scales are not configured with a VU meter scale.

Andy.

[Sergeauckland]

Originally Posted by Diabolical Artificer

I have a lot of experience with fitting "VU" meters to DIY amps. I've always built my VU own meter driver boards but you can get cheap meters & driver board from the usual sources.

However there is a far easier way to do it using the attached circuit with vintage meters. It's just a few resistors and a germanium diode. You may need to alter the value of the 1k dropper, maybe the 390r too with the meters you use.

These won't be true VU meters though, just eye candy, for more info see - https://www.vintage-radio.net/forum/...d.php?t=206266

Lastly I have pairs of vintage meters if you need any. These are WW2 meters but the scales are not configured with a VU meter scale.

Andy.

One issue that may or may not matter with the circuit given above is that using only half-wave rectification, there may be some significant second harmonic distortion introduced depending on the output impedance of the amplifier. An amplifier with a very low output impedance won't see much change in distortion, whereas one with significant output impedance, like a valve amplifier, will show more. However as valve amplifiers tend to have higher distortion anyway, it may not be significant, which is why I preface this by saying it may or may not matter.

Also, except for eye candy, VU meters are Virtually Useless for the purpose as they won't indicate clipping and only indicate average rather than peak levels.
A PPM is a much better way of indicating a much truer output level, but is a lot more complex.

S.

[Westo091946]

The Progress is a bit slow at the moment as the Component board I have shown (Photograph) I am not happy with the hole though rivet's which are slightly too long have a bit of a messy flair on the underside of the board, so redoing this only just received the new ones which are much smaller in length, so another set of 60 odd holes to drill and punch, ordering a chassis and base plate from the US the exact same size as original in aluminium and a base cover, will use self adessive film used for covering work tops which is rated to 70 degrees C to cover the chassis available in lots of colours.
Will keep you posted. Thanks for the input about the UV meters. Sorry things are only slowly progressing.