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Old 25th May 2019, 4:19 pm   #1
trabant
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Default Philips 575A suitable output valve replacement help required

During the week I bought a big pile of sets from Kalee99 including a Philips 575a which I'm hoping to restore in the next few weeks the set of course originally had an AC044 output valve this of course has been pinched by some git. I'd like suggestions for a not too pricey valve preferably that looks correct and how.to modify the circuit for it.
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Old 25th May 2019, 4:35 pm   #2
Hoveradio
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Default Re: Philips 575A suitable output valve replacement help required

I've just finished restoring a Bush PB65 that I bought at the Radiophile auction last Sunday.Of course the ACO44 was missing.I have fitted a PM24M valve and soldered the screen pin(centre pin 5) to the anode connection to run it in triode mode.Seems to work ok,lots of volume from the ten inch speaker.
Bias seems ok although the first valve that I fitted went a bit hummy and I found it was drawing grid current.Second one seems ok so far.Might be the higher than spec anode volts it is running at(285v).
John.
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Old 25th May 2019, 5:11 pm   #3
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Default Re: Philips 575A suitable output valve replacement help required

I might have to look at this again as I now appear to have distortion on the output stage.May end up connecting as a pentode,ie tie the screen to HT instead of anode.
John.
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Old 25th May 2019, 5:52 pm   #4
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Default Re: Philips 575A suitable output valve replacement help required

Apparently, a triode-connected EL34 will work OK.

(OK, you still have heater-voltage issues to address).

Perhaps you could use a triode-connected N41 or KT41 ??
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Old 25th May 2019, 9:21 pm   #5
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Default Re: Philips 575A suitable output valve replacement help required

I think I have a couple of PM24Ms kicking about I was just worried about the bias and wether I should change it
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Old 26th May 2019, 12:28 am   #6
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Default Re: Philips 575A suitable output valve replacement help required

Could a Philips E443 be utilised ?
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Old 26th May 2019, 1:43 pm   #7
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Default Re: Philips 575A suitable output valve replacement help required

I think you may need to lose about 30v on the anode supply.The PM24M has a stated max of 250v and the ACO44 would have had 280v on the anode.
I think that's where I went wrong.I have now fitted a PM24A in pentode mode that has a 300v anode max and a 200v screen max. Fitting a weak rectifier has got the volts spot on but this is only going to be a temporary fix for now. I also fitted a B5 base to make things easier.

I believe that the E443 is very similar to the PM24M.
John.
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