Leak Stereo 20 Power Supply Choke?

[afroaudio]

I have recently been bitten by the tube bug and now have a couple of EL84 PP amps to restore. First up is an early Stereo 20 with 3921 OPTs - Date stamped on underside is March 25 1959.

I have what is apparently the correct circuit diagram for the early version and want to go through the restoration keeping close to the original but am open to make some small component "upgrades" if some small improvements can be had.

Leak Stereo 20 3921 OPT by Bregtje Cals, on Flickr

I plan to try 5751 tubes in place of ECC83s and probably a passive pre like the Luminous Audio Axiom or possibly make my own with an Alps pot etc.

My main question is whether it is worth fitting a power supply choke in place of the 100R resistor in the Stereo 20? Apparently there are benefits to be had from using something like this: 157Q Hammond Manufacturing | Mouser

 

[soundmotor]

I would not worry about the choke first, get the amp to sound the best first. There are some articles out there on feedback reduction which just about any Leak can benefit from IMO.

 

[vinylkid58]

My main question is whether it is worth fitting a power supply choke in place of the 100R resistor in the Stereo 20? Apparently there are benefits to be had from using something like this: 157Q Hammond Manufacturing | Mouser

Personally, I'd look for a choke with a higher current rating. The 157Q is only rated for 150ma.

jeff

 

[Tubologic]

And try to find a choke with a DCR as close as possible to 100 Ohms or you might end up with a too high B+ (which is already close to or exceeding the limits in most LEAK tube amps). Not much to gain by adding a choke (IMO) as the Stereo 20 is already quiet in its original configuration (provided that the filter caps are good) and the slightly better regulation will have little sonic impact anyway. LEAK amps are very (too) sensitive and will easily accomodate a passive preamp but then you should not modify the original circuit to lower the gain. Substituting 5751's for the ECC83/12AX7's will have very little effect (if any) on the overall gain of the amp.

 

[audiodon]

I didn't find a choke a valuable addition. The dropping resistor doesn't get too hot.

 

[Trio]

With the 6BQ5's for finals, a choke is not an absolute must have item in the power supply. A great deal also depends on what listening levels that you are going to be operating the amp at. A choke is useful if you plan on driving it hard, you have energy "stored" in the iron that you do not have available with an RC filter in the power supply.

At normal listening levels, it is not crucial to have as long as the RC filtering is adequate..

 

[ggizzy]

If you are going to run the Stereo 20 with a Leak preamp, I'd advise separating the octal umbilical as they ran HT, signal, ground and filament together with very little shielding. This helped me with aleviate some hum issues with a different Leak amp.

 

[afroaudio]

Thanks for replies gents! As others have suggested I will first get the amp recapped and resistors checked and up and running in a semi original state but with reduced feedback and some other small changes. I dont plan on using the Point One Stereo pre at all but may construct something with a simple Alps pot in a box or use a passive pre like the Luminous Audio Axiom. Also noted that with a passive pre it is probably pointless trying to reduce gain by using different tubes in the 12AX7 positions.. Have a lot to learn still, thanks for your help

 

[primosounds]

157Q Hammond Manufacturing | Mouser[/url]

With all due respect to others I would say that a choke would be a good addition to the amp. It would help to reduce the AC hum, provide some current regulation, and IME, a choke sounds better than a resistor. And IIRC doesn't other Leak amps include a choke in the power supply? But if you a rebuilding the amp it would be best if you get it running first and then add the choke later when you have everything is sorted. Good luck, primo

 

[jaymanaa]

Does this work with the Leak one pre?

 

[ggizzy]

Leak made several stereo preamps as well but I believe the OP said he wasn't going to be using a Leak pre.

 

[afroaudio]

Thanks again gents! Primo your sentiments echo some others I have heard but seems good advice to first get the amp running nicely with new resistors and caps and then try a choke later and see if any improvements can be achieved.

I will look for something around 4H, 250mA, DCR close to 100R.

Re the pre amp I have a Point One Stereo that came with the amp, funky looking but apparently even rebuilt they are nothing to write home about.