New old px4 amp

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steve s
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#1 New old px4 amp

Post by steve s »

Some of you may remember this case.
It came to our 1st meet at Eggborough, adorned with brass metal work and pretty crap output transformers.
It got rebuilt about 10 years ago for px25 output valves, sounding much better but did not get much use
Most of the internals have been stripped out since and the rest removed in Jan this year..
I fancied another px4 amp and over the last few years I have collected quite a few early globes which I want to try
This one is the usual birds nest under the bonnet, .. theres alot inside.. but sounds very well.. super sweet and detailed and very dynamic.
I've had it running a few weeks now but still have not tested the globe px4s.. tonight's job
It's running nickle anode st px4s and mid 1930s cosser 41mhl choke loaded drivers.
There's about 9 chokes in all from a single power supply 275 volt anode and 32ish on the grid so great for the 250v early px4s
It's sounding very good. Jazz at the pawn shop sounds like I'm a few tables back from the band. The bar staff are getting on my nerves
20200308_152255_copy_1280x960.jpg
20200308_152744_copy_1280x960.jpg
Wonder if the early valves will get me a better table.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
RhythMick
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#2 Re: New old px4 amp

Post by RhythMick »

Very nice. Next Owston?
Cressy Snr
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#3 Re: New old px4 amp

Post by Cressy Snr »

Shoddy! :mrgreen:
Sgt. Baker started talkin’ with a Bullhorn in his hand.
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Paul Barker
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#4 Re: New old px4 amp

Post by Paul Barker »

Do it man
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
steve s
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#5 Re: New old px4 amp

Post by steve s »

It's going to the Wigan show this weekend... all being well.
It worked fine from the off with the st shaped valves. But when I tried the early globe px4s they started getting a little hot. (Paranoia on my side) They have max diss of 12 watts and they were running close to 13 watts so I've spent the last couple of days messing
You know what it's like you change one thing and everything else moves in the amp, they are running just under 12watts now
The voltage/ resistors has been changed about a dozen times this last couple of days
One more change back to where i was earler, lowering the ht another 8 volts and it's done..
It's making a really nice sound. Sweet.. very sweet jazz sounds.. it seems to play everything I want.
There's not alot between the two valves types but these seem a little more... well more, just subtle differences but more musical if that make sense.

The anodes are about 1/4" wider than the later valves but still nickel..
I had not realised that half of my early globes are the very first ones and run at 200volts so I'm giving them a miss on this amp
20200308_165401_copy_768x910.jpg
Last edited by steve s on Wed Mar 11, 2020 9:44 am, edited 1 time in total.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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Dave the bass
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#6 Re: New old px4 amp

Post by Dave the bass »

Peto-shoddy!
"The fat bourgeois and his doppelganger"
steve s
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#7 Re: New old px4 amp

Post by steve s »

If you want shoddy...
20200311_135201_copy_600x800_copy_444x638.jpg
As in the real shoddy..

Sorted the voltage this morning, the pic is of it upside down.. and its been playing music for the last couple of hours like that so I can keep checking everything, all is stable ...
It's quiet except for the mains transformer which buzzes slightly
(well quite alot when upside down ) it sound like one of my a.c. heated amps.. but the speakers are just about silent.
I nearly took it out but I don't have another with the right voltages and with enough windings for Andrews power supplies etc. and it would have been a big job..
20200311_135251_copy_600x800.jpg
The power supply section
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
simon
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#8 Re: New old px4 amp

Post by simon »

We don't often get to see inside your amps Steve - bit of a confessional?
steve s
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#9 Re: New old px4 amp

Post by steve s »

simon wrote: Wed Mar 11, 2020 5:43 pm We don't often get to see inside your amps Steve - bit of a confessional?
Suppose you could see it that way Simon.. I've a little more time on my hands this last week
Just made a cover for the mains transformers and the big choke, it looks ok.. those big oil filled jobs dont look so smart, so it's getting more living room friendly.

a other pic later
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
steve s
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Location: east yorks

#10 Re: New old px4 amp

Post by steve s »

All finished with transformer cover rested in place.
It got a lovely sweet detailed sound.

But it's just been removed from my system theres a breadboard amp there now..
20200318_162757_copy_1024x768.jpg
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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