Partridge choke rewind in Europe?

[Gtr0]

Good Morning, Everyone.

Well, I did a terrible, stooopid, terrible thing... I took the chassis of my 1969 Laney LA60BL out for a bright cap change... grounding the B+ to the chassis in case there was a charge. Put the new cap in and fired it up like an ass without removing the ground... so the choke went up in smoke.

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.

At first I was just looking for the correct vintage replacement, but they are in extremely slim supply.

So, I am interested in getting this rewound... Does anyone know of a shop in Europe that could rewind this to whatever it's specs should be? I can't even find out any ionfo on the net using it's part number stamped on the side...

Partridge TG9688/H1482... or maybe it says T69688... hard to say. Image attached.

Additionally, I'd like to get a proper modern replacement in place for temporary use while waiting. Any recommendations?

Thanks!!

[tedmich]

Bad luck as thats a very rare amp! Any transformer winder can figure out what choke had internally (wire length/gauge) but it wont be easy or cheap. Sadly John Chambers and Champion Electronics in Nottingham UK seems to have closed up shop, as he wound some great transformers.

It makes sense to call Laney, as they will at least be able to tell you the value, and maybe suggest a replacement. It could have been worse and cooked the PT or OT!

[Helmholtz]

You might try this guy in Italy (I've only heard good things so far): https://shop.piemme-elektra.it/products/6945

A remark:
It is not a good idea to directly short a charged ecap. Discharge currents can be up to 50A and more, not good for the cap.
Using a discharge resistor of maybe 10K would have saved your choke from smoking.

[Chuck H]

Accidents happen. I'm remembering two occasions when I was frantically swapping test situations at my bench and ran my own prototype amp at full tilt with no load ("Hey, why does that look so goofy on the scope? Oh $h!t !!!") Fortunately that amp has an almost bullet proof 16xx series Hammond in it and nothing fried. And I did once blow up a nice pair of brown base Tesla OO el34's because I didn't take measurements before testing a triode/pentode switch. (POP! "Aw f**k !!!")

Having concerns about EXACTLY what happened to you I not only use a resistor and let it take the time it takes, I also remove the clips after discharging before proceeding. Sure a little back charge will surge up in the caps but not enough to electrocute me.

[Helmholtz]

Sure a little back charge will surge up in the caps but not enough to electrocute me.

Back charge is a consequence of too fast discharge.

[Chuck H]

Back charge is a consequence of too fast discharge.

I admit I'm usually in a hurry and I've never seen caps discharge to zero. I use the 10k resistor or I just alligator clip to one of the plate resistors (plate side) and chssis with any standby switch in play mode. When I say back charge I'm talking a couple or a few volts as compared to the measurement when the discharge circuit is clipped on. I've never seen power supply caps not do this.

[Helmholtz]

I admit I'm usually in a hurry and I've never seen caps discharge to zero. I use the 10k resistor or I just alligator clip to one of the plate resistors and ground with any standby switch in play mode. When I say back charge I'm talking a couple or a few volts as compared to when the discharge circuit is clipped on. I've never seen caps not do this.

Then you probably didn't wait long enough for the cap to fully discharge.
Back charge means a voltage re-appearing at the cap terminals after it was briefly shorted.

[tedmich]

Mend it Mark made a tool for this,
https://www.youtube.com/watch?v=pNkEchLQWDU
but the voltages aren't sufficient for tube amps. Electroboom of course uses the "meat shunt" method...

a very bright colored lead (neon yellow/orange) might help remind you to remove the jumpers but hind sight is 20:10

[Chuck H]

Then you probably didn't wait long enough for the cap to fully discharge.
Back charge means a voltage re-appearing at the cap terminals after it was briefly shorted.

Well of course I understand that or I wouldn't have mentioned the phenomenon. In this case I must stipulate that "shorted" does not have to mean a zero V contact because I do use a series resistance. There's always a little crawl up in voltage after the drain is removed. I don't abuse the caps and it always happens. Just between a couple and maybe ten volts. Other than waiting maybe overnight for the process this always happens. I have to assume it's a mechanism of the battery nature of the capacitors. And no, I don't wait a day after clippimg on a discharge circuit before working on an amplifier. I'll wager I'm not alone.

[Gtr0]

You might try this guy in Italy (I've only heard good things so far): https://shop.piemme-elektra.it/products/6945

A remark:
It is not a good idea to directly short a charged ecap. Discharge currents can be up to 50A and more, not good for the cap.
Using a discharge resistor of maybe 10K would have saved your choke from smoking.

I knew better but I did get into this bad habit because I do not use the standby switch on amps and found none of my particular group of amps to keep any meaningful charge when I operated this way.... but as scared as I am of electricity I should always play as if there was a full charge... I used to have a lead with a 2W 10k in there and one day it fell apart. I will certainly make up a new fresh one with some beefy 5 watters I have laying around!!!!!

Thanks for the link... I have some trannies from an Italian company called inmadout... they are great as far as I can tell and his trannies remain in my favorite sounding amp. I never thought of reaching out to him.... if the guy I dealt with is still there. BUT, that link looks like there is some good stuff there too! Thanks - I will look into it!

[Gtr0]

Accidents happen. I'm remembering two occasions when I was frantically swapping test situations at my bench and ran my own prototype amp at full tilt with no load ("Hey, why does that look so goofy on the scope? Oh $h!t !!!") Fortunately that amp has an almost bullet proof 16xx series Hammond in it and nothing fried. And I did once blow up a nice pair of brown base Tesla OO el34's because I didn't take measurements before testing a triode/pentode switch. (POP! "Aw f**k !!!")

Having concerns about EXACTLY what happened to you I not only use a resistor and let it take the time it takes, I also remove the clips after discharging before proceeding. Sure a little back charge will surge up in the caps but not enough to electrocute me.

Great idea... my problem is having a shelf full of chassis prototype like amps and leaving them grounded for months... then one day I decide to revisit it, and plug it in... usually remembering to pull that ground clip. usually.

[Gtr0]

Just as a side note...

One time I ordered a transformer set from a company and downloaded the datasheet from their site for the wiring colors etc... wired up the amp. During the testing phase I had preamp tubes installed. Turned the amp on, heard a small pop... tuned it off. The fuses exploded etc... it turned out that the datasheet from the website was sort of wrong in comparison to the trannies I had in my hands. In the online datasheet, power trafo secondaries (HT) were green and the heaters were pink. But after my investigation started, I found a NEW datasheet in the shipping box that had green as the heaters and pink as secondary HT.

So I fed however many hundreds of volts to the heaters and a few volts to the plates.

I distinctly remember wondering why the heater tap was so small compared to that beefy HT tap. pfff.

Of course now I always ignore the online datasheets and make sure I get something in the shipping box.

Oh yea. the preamp tubes no longer worked either .


Thanks everyone for the replies.

I will just email Laney to ask if they know of a good modern replacement and reach out to these links Helmholtz provided, or Savino at inmadout .... I'll get it sorted. Not sure what the cost would be, but I am prepared to pay a few hundred Euros to keep that iron in use.

[Chuck H]

Just as a side note...

One time I ordered a transformer set from a company and downloaded the datasheet from their site for the wiring colors etc... wired up the amp. During the testing phase I had preamp tubes installed. Turned the amp on, heard a small pop... tuned it off. The fuses exploded etc... it turned out that the datasheet from the website was sort of wrong in comparison to the trannies I had in my hands

FWIW it's not unheard of for transformers to have incorrect lead colors right from the manufacturer. I think we've all seen it. I have and I haven't bought that many transformers compared to some here. In my case it was incorrect secondary colors on an OT so a lot less of a problem as long as it gets detected. I remember years ago one maker of poular Fender replacement output transformers would install the brown and blue primary end leads willy nilly so everyone that used them had a fifty fifty chance of oscillation after install. Some people had already trimmed leads such that they couldn't swap them after finding the mistake without splicing more lead. Which is frowned upon because it's ugly if you're working on a classic.

[Helmholtz]

Well of course I understand that or I wouldn't have mentioned the phenomenon. In this case I must stipulate that "shorted" does not have to mean a zero V contact because I do use a series resistance. There's always a little crawl up in voltage after the drain is removed. I don't abuse the caps and it always happens. Just between a couple and maybe ten volts. Other than waiting maybe overnight for the process this always happens. I have to assume it's a mechanism of the battery nature of the capacitors. And no, I don't wait a day after clippimg on a discharge circuit before working on an amplifier. I'll wager I'm not alone.

Being an experimental physicist I just had to do the experiment.
I charged a 47µ cap to 300V using a lab supply and a 10k series resistor.
After disconnecting the suppy I discharged the cap via the 10k resistor.
It took about 2s to drop the voltage to below 1V and another 5min to get below 5mV.
I then disconnected the load (and the meter) and sporadically checked the voltage at the cap terminals.
Within the next 3h a voltage of 7V built up.
When I left the voltmeter connected (corresponding to a load of 10M) max. voltage was only 3.5V.

[Chuck H]

Ah. Cool. That would be consistent with what I've seen. Mostly anyway. I'm distinctly NOT a physicist but I do think this is odd behavior without having two different metals (potentials?) in the construction. Being of a more mechanical mind this is a battery effect that shouldn't happen. Perhaps it has to do with changes in the oxides themselves.?.