Remember These?

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Cressy Snr
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#661 Re: Remember These?

Post by Cressy Snr »

Here is what I did, from earlier in the thread.
I put a 2.7R 3W wirewound resistor right up against the anode tag; no ferrite.
The ferrites went on behind the grid stopper as detailed below
Cressy Snr wrote: Mon Jun 03, 2019 10:00 pm
Mike H wrote: Mon Jun 03, 2019 9:30 pm Worth a sperrymint, if only to tick that off as having been tried. Only 3 things can happen, A. nothing, B. it makes it worse, C. it makes it better. You might need an oscilloscope to detect what's going on though, if not audibly obvious.
OK
So what I did is this:
Grid stopper up against tag as normal
ferrite placed on grid feed wire
feed wire soldered to other end of resistor as close to resistor body as possible
any protruding wire cut off with flush cutting pliers.
Ferrite slid up wire until it is as close to resistor body as possible with a kink to keep it from sliding back along wire.
Resistor and ferrite end up at 90 degrees to each other

Result!
I also grounded the heater centre tap tag on the 13E1 socket too. Noise was reduced further.
If you are using one 25V transformer heater winding per valve, ground the centre tap socket tag on each valve. If you are only using 1 heater winding, to feed both valves, only ground the centre tap tag on one of the 13E1.
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Ray P
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#662 Re: Remember These?

Post by Ray P »

Doh!

Thanks Steve; that shows the pitfalls of typing about something from memory and not looking hard enough!

Ray
Sorry, I couldn't resist!
Cressy Snr
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#663 Re: Remember These?

Post by Cressy Snr »

Oh pooh!

Listening this afternoon and the music gently faded out. Looking at the 6H30s there were no heaters, although the blue LED was lit on the DC module. Leaving things to cool, the heaters came back, only to fade away again about 15 mins later. Looks like the regulator is going into thermal shutdown. The heatsink was stinking hot when examined, and so were the three smoothing caps on the PCB.

On closer inspection, the reg chip is light grey when it used to be almost black. The lettering is non existent and the once white top hat washer isolating the reg from the heatsink is scorched to buggery. Clearly the poor thing has been thrashed to death.

Looks like a change of heater transformer and a change to AC heaters is going to have to be made, to get the OTL going again.
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Paul Barker
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#664 Re: Remember These?

Post by Paul Barker »

Not too bad, and sounds like you have a plaan.
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Ray P
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#665 Re: Remember These?

Post by Ray P »

Cressy Snr wrote: Sat Aug 24, 2019 6:57 pm Looks like a change of heater transformer and a change to AC heaters is going to have to be made, to get the OTL going again.
That's a shame Steve. What DC supply arrangements are/were you using?
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Ray P
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#666 Re: Remember These?

Post by Ray P »

If it helps, I think I have a couple of spare PCBs for these regulators that you're welcome to. Nice and compact at 50mm x 50mm. I'm using a couple in my build, running off 7V secondaries and using the chassis to heatsink the regulator devices.

https://www.diyaudio.com/forums/group-b ... t1083.html
Sorry, I couldn't resist!
Cressy Snr
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#667 Re: Remember These?

Post by Cressy Snr »

Paul Barker wrote: Sat Aug 24, 2019 7:34 pm Not too bad, and sounds like you have a plaan.
Yep, got it going again with an hour’s work swapping out the 9V heater transformer, running new heater wires to the 6H30pi sockets and the indicator light.
Ray P wrote: Sat Aug 24, 2019 9:13 pm
That's a shame Steve. What DC supply arrangements are/were you using?
I was using an old DIYHiFiSupply DHT filament supply module, on the 6H30s. It wimped out in the end. running off a 9V transformer, which was the lowest I had; not low enough as it turned out.

Anyhow, there’s still no hum, and no ill effects on the sound, so no harm done. :)
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Cressy Snr
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#668 Re: Remember These?

Post by Cressy Snr »

Ray P wrote: Sat Aug 24, 2019 9:27 pm If it helps, I think I have a couple of spare PCBs for these regulators that you're welcome to. Nice and compact at 50mm x 50mm. I'm using a couple in my build, running off 7V secondaries and using the chassis to heatsink the regulator devices.

https://www.diyaudio.com/forums/group-b ... t1083.html
Thanks Ray, but the amp is working nicely now, so no DC needed. :)
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Cressy Snr
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#669 Re: Remember These?

Post by Cressy Snr »

It’d be the usual cliché to say that the sound is more “organic” with the AC heating, and it is. But in my case, the DC was applied badly so the comparison isn’t worth the web page it’s written on.
Anyway; that’s my story and I’m sticking to it. :mrgreen:
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Cressy Snr
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#670 Re: Remember These?

Post by Cressy Snr »

A nice little mod today:
The single 250K stereo TOCOS volume pot, has been replaced with my pair of early 1960s, NOS, switched Allen Bradley 250K mono pots.
These old carbon pots last made an appearance on the pair of 2A3 monoblocks, I built in 2010, on a pair of aluminium guitar amp chassis. That pair of amps was, until I built this OTL, the best sounding thing I’d done, and rather foolishly, as usual, I dismantled the things.

I had thought the control shafts on the pots would be too short to fit anything to, as the controls on the OTL, mount to a plate behind the half-inch thick, wooden front panel, whereas on the 2A3s, they mounted straight to the casing. But it turned out that there was more than enough metal protruding beyond the plane of the front panel to be able mount the two control knobs without any slack or rocking.

In terms of sound quality, the upshot seems to be, that a quite a lot of the characteristic sound of that pair of 2A3 monoblocks was down to these pots. In the OTL they take the sound to a nice place. The tone of midrange instruments and voices is beautiful, and the treble is detailed and sweet; like a good valve amp should be.

These pots need to be cared for. I have a pair of 50K ones, of the same make and vintage, with 3” long shafts, and judging by the sound of the 250K ones, I need to seal these 50K buggers in a bag, not have them knocking around in a scruffy old parts box.
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Cressy Snr
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#671 Re: Remember These?

Post by Cressy Snr »

Image
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Cressy Snr
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#672 Re: Remember These?

Post by Cressy Snr »

Drunk again posting pics with no explanation. :lol:

Lot of work went on under the hood last week; plenty of cutting, drilling, filing, bleeding and getting zapped by 2200uF capacitors. It’s a rebuild of the whole of the power supply.
Originally it was just a copy of Bruce Rozenblit’s Mini-Beast PSU setup, intended as a “get you going” arrangement.
Now it’s not :wink:
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pre65
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#673 Re: Remember These?

Post by pre65 »

Are tory voters allowed to know whats been done and how you like (or not) the result ? :lol:
The only thing necessary for the triumph of evil is for good men to do nothing.

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Cressy Snr
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#674 Re: Remember These?

Post by Cressy Snr »

Image

No! :mrgreen:
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pre65
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#675 Re: Remember These?

Post by pre65 »

Nice one Steve. :)
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
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