PYE 15A valve question
 

Hi there as I am a newbie to radio restoration I hope you will bear with my general lack of knowledge. Hope some one can help with this. I have bought a PYE 15A circa 1945 to restore the problem is the EBL31 valve is missing unfortunately some one has forced in at least one other valve resulting in no less than three locating slots has any one a photo or diagram of the orientation to fit the valve.Many thanks best regards Ron H.

Re: PYE 15A valve question
 

You could always check for 6.3 volts AC on pins 2 and 7, this would enable you to insert it correctly although I cannot see how it could have been inserted incorrectly without damage to the valve spigot.

Added chassis pic for easier clarity

Re: PYE 15A valve question
 

Trader sheet 751 shows the 'locator' pointing to the valve holder rivet, by the 3 of V3. Same as V2 (the EF39 holder) orientation.

I would do the check as Freya suggests to be sure. Use V2 as the guide to which are 2 and 7...

Re: PYE 15A valve question
 

Thank you Freya /snowman I think what Freya was saying was how could the valve be inserted incorrectly what seems to have gone wrong is at least two incorrect valves have been inserted at some time and new key slots have been filed in so there is a choice of three positions and as of yet i have not located a ebl 31 replacement but from what i understand these are not cheap so i don't want to blow it by putting it in the wrong location. Once again thank you for your time and trouble to get back to a learning novice. Best regards Ron H.

Re: PYE 15A valve question
 

Hi Ronners,
I have never seen a 15A, but wonder if the valve holders (sockets) are the thin brown paxilon type?
The paxilon type are very brittle and it is easy to 'make' another key way if you do not understand the need to line the key on the valve spigot with the recess in the holder... the valve spigot key always wins!

As you say an EBL31 is hard to find and someone might have tried a substitute, but that would need changes to the circuit. Have a look under the chassis and see if there are any obvious changes.
But the common thing about octal valves is nearly all have their heaters on pins 2 and 7. So just making another key way by 'design' to fit a substitute is not going to work.

You have a PM. Alan

Re: PYE 15A valve question
 

One of my favorite sets.

The valve holders are indeed paxolin ones.

Just to help Ron, valve pins are counted, looking underneath, clockwise from the spigot.

On the Pye 15A pin 2 is connected to the chassis. Pin 7 is connected to each valve by a black wire and at the EBL31 there is a thick wire from the transformer.

I may be able to help if you get stuck for an EBL31

Re: PYE 15A valve question
 

Many thanks for all your help I think you have pointed me in the right direction.

Best regards Ron H.

Re: PYE 15A valve question
 

Hi!

EBL31 pinout & data:–

1 – i.c., 2 – h, 3 – a, 4 – ad', 5 – ad", 6 – g2, 7 – h, 8 – k, g3, cap g1

Va 250, Vg2 250, Ia 40mA, Ig2 4mA, G.B. –7.5V, gm 9.5mA/V, Ra 6500 ohms, Po 4.0W for 10% THD. Rk 150R

EBL31 circuits can look a little off–putting because they have the diode anodes on P4 & P5 connected to the 2nd IFT and A.G.C., with a meshwork of r.f. filter and detector load components that all had to be returned to pin 8 (k) with (often) a tapped cathode–bias resistor for A.G.C. bias/delay purposes, which makes the whole diagram look like a Chinese puzzle, as it was very uncommon to draw the two diodes of an EBL31 etc., type of valve separately in those days!

However, being a "short" superhet you don't have "that" cap to worry about as the top–cap grid of the EBL31 will be returned to chassis via the volume control, which normally is only connected to the diode load, so any unwanted bias will be in a negative rather than a positive direction, so altho' you might get low volume if the volume control d.c. isolating caps leak, it shouldn't put the EBL31 at risk, but do NOT run the set with the EBL31 top cap connector removed – short the top cap to chassis with a 100k resistor if you do have to remove it to test for hum etc!

Chris Williams

Re: PYE 15A valve question
 

I used to own one of these many years ago. it was a nice set and performed very well. I seem to remember it has an extra feedback winding on the OPT as well.

Re: PYE 15A valve question
 

The 15A was a lovely set. I have one in my collection, plus another one in the loft awaiting attention.

EBL31 valves are fairly easily and cheaply obtainable nowadays, alternatively EBL1 valves are also easy to get - they have identical characteristics and you could either make up an adaptor using the base off a dud octal valve and a side contact valveholder, or if you are happy doing fine soldering work, actually remove the side contact base and replace it with an octal base. I have done this, though it is very fiddly.

However, the fact that the valveholder has been tampered with suggests that some other valve has been used in place of the original one. Something like a 6V6, for example - but unless the replacement valve had internal diodes, you may well find that solid state diodes have been soldered into the valve holder.

If you want to keep it original (or return it to its original specs) I would replace the valve holder as well as fitting a new valve. It would be sensible to replace C18 (Trader sheet 751) as well.

Re: PYE 15A valve question
 

If you do go with a pentode + two diodes fix, use a valve with a highish gm like the EBL31 has. A 6V6 isn't a brilliant choice here, its other desirable properties notwithstanding.