Author Topic: Leak Stereo 20 restoration/mods  (Read 11644 times)

Offline Ampdog

Re: Leak Stereo 20 restoration/mods
« Reply #30 on: June 25, 2015, 01:58:31 AM »
As indicated earlier, no diagram differences, only component values:

R5:  100K,  47K
R12, R13:  1M,  470K
C5:   20N,  100N
Transformer secondary:  300V,   280V

The latter values as indicated on the last schematic given by Afroaudio is the latter version. As said, there were too many EL84 failures from G1 run-away with the 1M values and they were forced to lower that. The values were still within the specs for EL84 though the upper limit - apparently that limit was/is ambitious, or the slightly higher than spec.ed h.t. voltage caused trouble, or both. This was also lowered. (The EL84s are running om maximum dissipation, so with some rise in the mains voltage or the wrong tap .... )
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Ampdog

Re: Leak Stereo 20 restoration/mods
« Reply #31 on: June 25, 2015, 02:17:58 AM »
I promised an alternative for those who find the 70 mV input sensitivity to much.

By removing C2 the loop gain is lowered (current degeneration in the first stage) and NFB restored by lowering R18 to 5,6K and increasing C5 to 270pF to maintain stability.  The input then becomes 200 mV.rms for full output, perhaps more managable with high intput signals. This could be further increased by replacing V1 with an ECC81, but one then has to also slightly change R2 etc. This is going away from the original and I did not investigate this, though I personally would rather have used an ECC81 (12AT7) to begin with.

There is a further option to make the output 'stiffer', but let us not deviate too far from the original.                                                               
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline TriodeFan

Re: Leak Stereo 20 restoration/mods
« Reply #32 on: October 25, 2016, 01:41:45 PM »
The couple caps (i think Leak used PIO) may give the 'right' sound, but are know to leak, and that can cause trouble ... best to replace them!