The Amp Garage

This is measured AC voltage n cathodes. ie current on 1ohm resistor in cathode?

Change place of output tubes in sockets from 1-2 to 3-4

There should be no drama around that...electrolytics working on low temperature, in everyday use can last more than 100.000h..maybe also 250.000.. so 30-50 years.. it is no miracle that amps from 70ties still working. If temperature is increased, life is shortened very much. If elco is NOT working o...

WhopperPlate wrote: ↑Sat Jun 01, 2024 4:04 pm

bepone wrote: ↑Fri May 31, 2024 7:21 am for Marshall metal film and polypropilenes should be avoided because result is awful .. been there... recipe is carbon film + polyester

There he is, the guy I warned you all about ! Do not listen to him !

never

Roe wrote: ↑Sat Jun 01, 2024 7:21 pm

bepone wrote: ↑Fri May 31, 2024 7:26 am Metroamp also added few metal oxide resistors 3W in their version, maybe for a reason

they used 2w MOs for voltage dropping in the power supply. but the MOs do not sound as good as CF or CC here

in signal: cathodes 2. stage , 820R and 100k and NFB MOX

usually tube is microphonic in stage where is maximum gain..and input signal very low... V1 position.. tube rolling can help.. also adding grid stopper too.. microphonic tube shift to PI position, and some short plate 12AX7 to V1..

Metroamp also added few metal oxide resistors 3W in their version, maybe for a reason

bepone wrote: ↑Fri May 31, 2024 7:19 am it is possible to change few components without major change in the sound, because all together it counts..there are many compoents in the group at the end.. so if something is missing regular carbon film will be ok (modern cheap SR Passives or TE )

ofcourse 1-2W not less

for Marshall metal film and polypropilenes should be avoided because result is awful .. been there... recipe is carbon film + polyester

it is possible to change few components without major change in the sound, because all together it counts..there are many compoents in the group at the end.. so if something is missing regular carbon film will be ok (modern cheap SR Passives or TE )

1. internal tube structure problem, some bad assembly, then arcing internally..

2. on sockets because of flux between in 2 and 3, which with time strting to be conductive.

3. because of bad sockets, porosity in materials and humidity

Me too. But prices are too high... so i changed, i have luck nowadays with axial TAD Mustard caps (probably also chinese, cheap, but sounding very nice), looks good too

edit, this post on top is for working amp here is major problem short circuit to the ground on Ub+ line, so new procedure: 1. switch off the amp 2. drain all the capacitors , with 10k to the ground until discharges 3. multimeter in ohms, and touch every node on + cap and to the ground, find out whic...

1. remove feedback wire from the speaker terminal

2. start amp again

3. if there is no any noise and amp works, switch off

4. change anode wires from OT to pins 3 - sockets, A1 <-> A2

5. start amp again, verify all is correct

font , colors, quite bad printing and shape looks like Sozo

1mV AC balance on cathodes? this is negligible... also 2mV is negligible (impossible to hear that), i would leave this like it is