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Old 23rd Feb 2021, 10:33 am   #1
RobertFM
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Default Pye 75 valve line up

I acquired a PyeP75 last year that was rescued from a house fire. It was too smokey to be allowed into my house. A few months in cold draughty workshop over the winter has allowed the pong to evaporate, and I brought it into the house to have a look at it.

V5 as per the Traders sheet 1135 should be an EZ41. In the set I have it currently has an EL41 instead. Valves 1-4 are correct.

Is an EL41 an acceptable substitution for an EZ41 here ?

The set looks unmolested - still with waxed paper caps.

Any thoughts ?

Robert
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Old 23rd Feb 2021, 10:42 am   #2
ms660
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Default Re: Pye 75 valve line up

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Originally Posted by RobertFM View Post
V5 as per the Traders sheet 1135 should be an EZ41. In the set I have it currently has an EL41 instead. Valves 1-4 are correct.

Is an EL41 an acceptable substitution for an EZ41 here ?
Definitely not.

Lawrence.
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Old 23rd Feb 2021, 11:05 am   #3
RobertFM
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Default Re: Pye 75 valve line up

Thats what I was looking for !

Clear, concise advice.

I'll source a replacement EZ41 .

Many thanks.

Robert
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Old 23rd Feb 2021, 12:07 pm   #4
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Default Re: Pye 75 valve line up

EZ41 is an HT rectifier. You would find one connected to a mains transformer: a centre-tapped high voltage winding feeding current to the anodes, and possibly a separate heater winding for it or maybe it s heater runs with the rest of the valves. EZ41 is said to have initially been for car radios, so the heater-cathode insulation ought to be good.

EL41 is an audio output pentode. You would find one connected to the output transformer and thence the speaker.

The Pye P75 needs one of each.

David
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Old 23rd Feb 2021, 12:16 pm   #5
RobertFM
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Default Re: Pye 75 valve line up

Yes - that ties in with what I had surmised from my attempt at understanding what I have read here and elsewhere.

It does of course beg the question of what the EL41 is doing at V5 ?

Would the radio ever have worked with it there ?

Robert
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Old 23rd Feb 2021, 12:28 pm   #6
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Default Re: Pye 75 valve line up

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Would the radio ever have worked with it there?

Robert
No it wouldn't work. Finding valves in the wrong position or of the wrong type is nothing unusual. It's likely the rectifier was filched and someone put whatever they had in the socket to make the set look complete. I've come across a lot of sets with missing rectifiers.
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Old 23rd Feb 2021, 2:21 pm   #7
RobertFM
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Default Re: Pye 75 valve line up

OK, thats all very helpful.

Many thanks.

Robert
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Old 23rd Feb 2021, 7:40 pm   #8
Chris55000
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Default Re: Pye 75 valve line up

Hi!

I had a P75 when I was younger, and the correct h.t. rectifier should be an EZ40 if an EL41 output valve is in use as the 60mA maximum current rating of the EZ41 is only just adequate to cover the h.t. current of the set, however, if you reduce the anode current of V4 (EL41) by inserting a 5k6 2W resistor between pin 5 (g2) of V4 and the main h.t. line, this will reduce the total h.t. current to within the EZ41's rated 60mA with a bit to spare!

Chris Williams
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Old 23rd Feb 2021, 8:18 pm   #9
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Default Re: Pye 75 valve line up

The EZ41 is well within it's ratings according to a schematic I'm looking at (Pye P75) The rectifiers load current is given as 36mA unless it's a mistake.

Lawrence.
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Old 23rd Feb 2021, 10:40 pm   #10
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Default Re: Pye 75 valve line up

This prompted a quick look at EZ41 vs EL41 base connections.....

A direct sub would probably not work since one of the ac inputs would go to the control grid of the EL41, though if this didn't arc over or indeed did and evaporated the grid then it just might, since the other ac input will go to the EL41 anode and the cathode and heaters are on the same pins anyway. Not recommended but might just work as an emergency bodge

A further furkle with me bodger's 'at on suggests that you probably would get away with subbing a UY41 with a UL41, for a while at least
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