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Old 3rd Mar 2010, 10:24 am   #1
Neil Purling
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Default FrankenPye

The beginning was when a carrier delivered a big parcel from Past Times Radio.
I bought the mortal remains of a Pye 15A, first marketed in 1946. I feel mine is rather later as early examples used military surplus components.
I got a partially stripped chassis only. The case was long gone, and other people had already claimed the field-coil speaker, the mains and the output transformer.
This is why I placed my report in this section because of the improvisation & bodgery that has taken place.

The most important place to start is the power supply & here it was entirely missing apart from the dual 8/16 uf electrolytic. I got my patent re-former down from the loft, to see if it would re-form or not.
Well, one section would but the other leaked persistently. As soon as I took it out I could see something had literally leaked out past the seal in the end of the can.
The new PSU came from member Ed Dinning. The transformer is a massive shrouded example, more often seen on a audio amplifier. This has a centre-tapped LT winding for the main heater chain.The rectifier winding was modified to suit my intended use of a EZ81. Mr Dinning also provided a choke to go in place of the field coil of the speaker which performed the same function. He also provided a exact replacement 8/16 uf electrolytic.

The chassis contained several waxed paper capacitors by Dubilier & Hunts. I ordered replacements from a vendor in a former Soviet Republic. The Russian capacitors are also allegedly paper-in-oil to military specifications. All I know is that I have used them before without any problems.
At that point I had to wait for delivery, which was a extended wait because of Christmas.

The next installment involves the use of saws & hammers. Those of a nervous disposition are warned..............
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Old 3rd Mar 2010, 9:22 pm   #2
Neil Purling
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Default Re: FrankenPye

While I waited for the postal service to deliver the capacitors I needed to extend the Pye chassis to receive the outsize mains transformer. I obtained a stripped out chassis of the 45A, its AC/DC brother.
This was the bare steel box only. I took one end of that, plus some other small bits of steel. I used those small bits of steel like fish-plates to attach the extension with many 3mm bolts. I also made some extra holes with a chassis punch for cable routing. It sounds simple, just a sentence which represents a mornings work with a hacksaw (with two nicks in the blade), G cramp, file and hammer. Pye used good steel for the chassis.

The electronic work started with re-wiring the heater chain. The valves follow the usual convention with International Octal based valves of having pins 2 & 7 for the heaters. Here pin #2 was wired to the chassis, which had to change because of the centre-tapped heater winding.
The mains switch of the Pye 15A is mounted on the back of the tone switch array. It is a double-pole switch, but strangely only one side was used. I wired both pairs of contacts. I wanted to measure off-load voltages so I switched on.... CRACK. Instantly the precautionary fuse I fitted to the Primary of the transformer bit the dust.
One set of contacts shorted to the other side when the switch was thrown. I raked through my boxes for a toggle-switch instead.
Those Russian capacitors are almost the same phycical size as the originals so they even slid under the original holding clips.
The power supply is protected with a 1A fuse in the primary winding. The EZ81 rectifier is protected by 1A fuses each side of the centre-tap.
The RF side & IF strip would be left well alone apart from lifting the 1st IFT out to replace the fly-lead which would connect to the top cap of the EF39 IF amplifier. I was careful to photograph the wiring to the IFT before I un-soldered anything.

The output valve in the Pye 15A is a EBL31. Now why they didn't use the standard conventional 'long superhet' complement of ECH35, EF39, EBC33 & 6V6 I don't know. You can buy replacement EBL31's, which aren't too expensive, but they are Continental examples by Phillips converted from EBL1's.
The extra height compared to a Mullard original is 3/4". It went against the grain to fork out £22 for one valve.
I now know that a forum member has engineered a substitute involving a EL84 and diodes, which I am not capable of following because it involved use of a lathe. I had to change the top cap connection because the Phillips EBL31 top cap is the larger diameter type.

My work so far was rather cautions, a couple of hours here and there & I made a mistake.
When I fitted all the valves and powered up the heaters lit, there was HT in all the right places but there was silence. I hauled out my Gould 'scope. There was signal on the grid of the mixer & the grid of the IF amplifier.
What was wrong? The HT was rather high at 300V. A touch to the EBL31 top cap barely gave a buzz at all. Clearly it was not drawing any current so I started to poke about the valve base of the EBL31 and realised what i'd done.........
In changing the power supply arrangement I had clipped out a wire feeding the screen grid of the EBL31, so there was 0V there. A slight curse later I wired the screen to the HT line as it ought to have been.
On the second try HT was normal, but only audio was a slight motorboat. I swopped the Frequency Changer and IF amp for a clear glass 6K8 & 6K7G and it shrieked like a Banshee.
Substituting the plain glass valves for metal coated ECH35 & EF39 procuced nice audio (Bucharest, Romania on Short Wave), but it easily fell into oscillation.

Now there I really was stuck. I tried spraying all the switches with Servisol 10 with no effect on the oscillation.
A local member whom i'd exchanged PM's about the EBL31 offered to assist me.
Some of my wiring left a bit to be desired, a opinion I agreed with, it could do to be tidied.
The cause of the oscillation seemed to be physical. I could switch on, the set played normally until I either used any of the switches or we tramped up and down his shack. It misbehaved once and refused to oscillate again.
We compared EBL31's and tried his EL84 adapter, which was a effective solution.

Of course.... When I got it home it was up to it's tricks again. In the end I bought some Caig Deoxit after seeing mention of it on this forum and dosed the switches and valve bases with said juice. The valve bases are fairly simple affairs and that holding the ECH35 frequency changer wasn't holding the valve too tightly so I changed the valve base for a NOS Mc Murdo one. It held the ECH35 in a vise grip but the set was still unstable.
I had assumed that the problem was in the mixer stage, because there was no oscillation if I removed the top cap off the EF39 IF amp. I think the issue was that the EF39 I had substituted for the clear glass 6K7G had a defective contact between the metalised coat and pin #1. I have plenty of EF39's. I substituted a WW2 era Mullard EF39 in VR53 Air Ministry guise.

I am happy to report that All is now as it should be. The EBL31 supplies more than enough power to my Celestion extension speaker to be intolerable on full throttle for more than a few seconds. The Raymond case being bakelite lacks bottom end.
The Pye rotary switch tone control only made the sound more muffled so I removed it. I . There is also no cathode bypass capacitor on the EBL31.
I had a Jackson dial and ball bearing 6:1/36:1 drive which made it possible to tune Short Wave without needing Artful Dodger's dexterity on the tuning knob.
I think it does need a dial lamp. I have a MES bulb holder somewhere.

The electronic design is still Pye original as far as the output stage where I have got creative out of necessity.
The power supply is way better than the original equipment. The substitute mains transformer almost doubles the weight of the chassis.
I have no plans to encase this project at present. I have tidied the wiring to reduce hum, which is still present.
Maybe the re-formed replacement electrolytic is not quite up to the job. I have a pair of German F&T electrolytics from the BVWS Spares Dept just in case a change is warrented.
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Old 3rd Mar 2010, 10:09 pm   #3
AlanBeckett
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Default Re: FrankenPye

Quote:
Originally Posted by Neil Purling View Post
... conventional 'long superhet' complement of ECH35, EF39, EBC33 & 6V6 I don't know..
What? For a Pye? An American 'tube' It would be an EL33 surely for the output.
Being a Pye person I regard this Thread as a 'Cruel and Unusual Punishment'
One of these days I must get that 39J/H chassis out of the attic and do something with it.
Alan
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Old 3rd Mar 2010, 10:34 pm   #4
Sean Williams
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Default Re: FrankenPye

Quote:
Originally Posted by AlanBeckett View Post
Being a Pye person I regard this Thread as a 'Cruel and Unusual Punishment'
Whats cruel and unusual about taking two scrap chassis, and learning from them?

A good attempt Neil - Chassis bashing is hard work, especially so if you have limited experience and tooling to work sheet metal - reusing a scrap chassis is probably the best solution to the problem!

Looks like you have had fun with this project

Sean
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Old 4th Mar 2010, 9:05 pm   #5
Neil Purling
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Default Re: FrankenPye

I think Alan was more offended by the idea of using a valve of American origin in a English radio rather than the creative metalwork I indulged in.
If you have got a orphan chassis then there is damn all you can do about it unless you are a cabinet maker or have a empty case squirelled away.
I feel that the fate of the Pye 15A chassis would have been to be slowly stripped of anything remotely useful. Now, it has come back to life.
Short Wave is still interesting. Last night I was listening to Gregorian Chant from Vatican Radio. Problem is I have no clue as to the wave length. I never, ever had the dial. The Short Wave coverage is mentioned as 16m -52m, so I figure the reception of Vatican Radio was in the 49m band as the var capacitor vanes were almost totally meshed.
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