Partridge choke rewind in Europe?

[Greg Robinson]

The phenomenon is called dielectric absorption. The wikipedia article is as good a place to start as anywhere.

[Helmholtz]

No, it's not a battery effect. No 2 different metals in an AL cap.
The effect is called Dielectric Absorption or Dielectric Relaxation
https://en.wikipedia.org/wiki/Dielectric_absorption
(I love Wikipedia and use it all the time.)

Edit: Greg Robinson beat me to it.

[Helmholtz]

The principle of DA can be understood by imagining a large cap having a low ESR in parallel with another cap having a very high ESR (Megohms).
When shorted, the main cap will discharge quickly to 0V, but the other cap having a very long discharge time constant will still hold a charge.
When the load is removed, the charged cap starts to slowly recharge the discharged one.

[trobbins]

I placed a 5 henry 150mA or so choke in it's place (intended for a Superlead) as a temporary fix, but the low end crackles on some semblance of a "chug" on bass heavy notes, or rather the vintage amp version of a "chug"... and so I hope it's because the choke can't handle the amount of power needed for this amp... but to be honest, I am not as educated as I'd like to be... learning by doing and reading... The B+ at the choke is usually around 560 V or so iirc.

There are two schematics in this link thread on EL34world. If your LA60BL is similar, with the choke supplying the screens and pre stages, then 150mA rated choke should be quite sufficient. One schematic indicates 20H, so 5H may be noticeable if there is no filter cap on the screen. I'm just a bit concerned that some other collateral damage may have occurred.

[Gtr0]

There are two schematics in this link thread on EL34world. If your LA60BL is similar, with the choke supplying the screens and pre stages, then 150mA rated choke should be quite sufficient. One schematic indicates 20H, so 5H may be noticeable if there is no filter cap on the screen. I'm just a bit concerned that some other collateral damage may have occurred.

Ah. Sorry to revive this like almost a year later... my problem as that I am into amps and modifying/building them as strictly a hobby... so while I love to learn about this stuff (just was reading your PDF file on the R3000 post #39 thread earlier this morning), between being a full time web developer and a touring musician, and a father, and owning a very old home etc etc, I end up basically forgetting everything I learned in 6 months unless I use it daily... okay, long winded sorry.

I couldn't find the link you spoke of, but I will attach the schematic I have that is very close. And the amp is very original except any electrolytic that were original were replaced and I moved v1a and v1b closer to super lead type specs. Which one day I will revert back to original.... oh yea, and I put in an adjustable bias circuit.

The sound... I should post a clip - I'll look for the one I had... it's not obvious... it doesn't happen unless I "drag" a palm mute... in other words, I I palm mute a bottom "E" power chord and let it hang a few seconds the crackle will appear... it sounds like digital distortion somehow and at first makes one think that the digital converters are being overloaded, but it is not the case. I should revisit it, it's been some time and I have sadly let the amp sit and have not moved to having the choke rewound yet. But still have this link Helmholz provided me.

Laney-60.pdf

[trobbins]

Using the schematic Laney 60 s/n 2X1511, perhaps you must have shorted screen supply 'B' to chassis in order to smoke the choke ?

If so, then it is plausible that there is some collateral damage related to the power transformer, or diodes. But I guess the symptoms could also be from blocking style distortion of the output stage.

Perhaps if you can drive the amp with a low frequency tone and turn the volume up to see if you can recreate any crackle condition then that may be a start to more focussed fault-finding.