Pye LV30 main resistor chain

[rogerdup]

Hello Everybody,
I was trying to find a nice assembly for replacing the open parts of the main resistor chain of the LV30. I finally found this solution: rewinding the 98 ohms section (25ohms/meter resistive wire) which become in fact 108 ohms to accomodate the voltage here. And fix a widap type 330 ohms 25w resistor on the new shield, this one made of pre-drilled aluminum plate. In the empty space left by the old 365 ohms section, I wound up to 35 ohms of wire (28ohm/m) put in serie of the widap to adjust the 365 ohms value in parallel to the CZ1.
All this is not being a big deal, but perhaps to give idea for those interested in this restoring job.
Another wounding approach: you want to fill the old space of the 365ohms, use the 28 ohms/m up to 145 ohms and replace the 330 widap by a 220 ohms. This if you like wounding resistive wire (. I think I will do that on the 365 ohms section later on.
Roger

[radiograham]

Hi Can I ask is the type of wire you use insulated. I noticed the windings are not spaced side by side so I presume this must be the case.

[1100 man]

Hi Roger,
I too would be very interested in knowing more about the different types of resistance wire available and your experiences with it. I have a need to wind a dropper for a TV but would need higher than 28 ohms/M wire.
Conventional droppers were covered in what seems to be some sort of ceramic coating. Have you found any way to reproduce this?
Many thanks for sharing your experiences
All the best
Nick

[FERNSEH]

Conrad-Electronic offer resistance wire in various ohms/M values.
An example: https://www.conrad-electronic.co.uk/...f=searchDetail

DFWB.

[rogerdup]

Hi gentlemen, David give the answer
In fact for the 365 ohms section of the bleeder, I used the 63ohm/m by Conrad, but this wire rapidly get overheated and begin to burn.
The Conrad 28ohm/m is not bad for rewinding the 98ohms section and seems to make the job without burning. This wire is constantan insulated.
I investigate on the net for values between 28ohm/m and 63ohm/m I could use for rewinding the 365 ohms section. Found nothing but 44ohm/m NOT insulated. All over 28 ohm/m are too thin for 300ma current.
I really don't know what kind of wire PYE used for the 365o section, but looking at part of the one remaining on the bleeder when I began my restoration, it was very thin. I don't know how long this wire stayed operative. Certainly worthwile for repair men.

[rogerdup]

After looking carefully at the 365 ohms section, I found that PYE should have used 52 turns of a 100 ohms/meter resistive wire for a value close to 365 ohms. The diameter of the wire appear to be close to 0,25 millimeters, over a width of about 30 millimeters. (sorry for all those french measurements). Now, finding a 100 ohms/meter wire with such 0,25 mm diameter is almost impossible..(PYE NOS?)
Have a nice week everybody !
Roger

[rogerdup]

Hello,
I am back with that rewinding stuff on the LV30 PYE main resistor.
I finished to repair the two open sections. see photos.
It has not been possible to rewind the 365 ohms section the same as the original, cause the wire used by PYE is no more available. As said in my previous message, the deal was to fill this section for the look and have it also operational.
Now I have the 98 ohms section wired with 28ohms/m up to 107 ohms.
The old 365 ohms section is wired with the the same 28ohms/m up to 145 ohms. On top of the new shield you can see the 220 ohms 25W resistor put in serie with the 145 ohms.
Also, I add two 8.2v zener on each side of the CRT heater to protect this beloved thing. I get a stable 6.2v all the time. Great !
Comments welcome !
Roger

[mark pirate]

I had the same O/C dropper problem with my LV51F (same chassis).
I was lucky enough to come across another dropper with the same values, I fitted it above the original one.

Mark

[rogerdup]

Yes it it is quick repair solution.
What section was open on your? I don't see your CZ thermistor?

[petertheorgan]

I am afraid I cheated , I made one up from RS " polomints "

[rogerdup]

Hi Peter,
I did not understood (my english is poor)
I saw on your profile that you are an organist.. Me too. Play sacral organ. Mine is the Vivaldi 150 by Johannus.
Roger

[mark pirate]

What section was open on your? I don't see your CZ thermistor?

All sections apart from one were open, the replacement dropper was from a later Murphy set.
I never thought of rewinding it at the time, if I had not found the dropper I would have used a few of those metal clad resistors.

Mark

[FERNSEH]

From the information in the Mullard Maintenance manual I find that the heater supply surge limiting thermistor employed in the Pye LV30 is likely to be a type VA1005. Looking at circuit diagrams of other Pye Group TV receivers such as the Invicta T120 and the Pye FV1 series, we find that these receivers also employ the VA1005 thermistor and like the LV30 a resistor of 350 ohms is connected in parallel with the VA1005.
However, another Pye group set, the PAM 954 the VA1005 is present in the heater chain but does not have the parallel resistor.
I'm of the opinion that the 365 ohm section can be dispensed with and the total heater current will flow through the thermistor.
An alternative thermistor is the Mullard VA1026 and this device does not require a parallel resistor.
The Ferranti model T143 employs the VA1005 without any parallel resistor.
Cossor 930, VA1005 with 500ohm resistor.

I don't have the specifications of the VA1005. I'd guess the resistance when cold is 5Kohms and will fall to 100 ohms or so with 0.3amp flowing through it.

DFWB.

[rogerdup]

Thank for those valuable informations David.
I should confess that up to now, I have not completely understood how the CZ1 and the 365 ohm resistor in parallel worked. Anyway, I found interesting to try an approach to the original mounting as I described.
My measurements on the CZ1 alone give 487 ohms cold and 110 ohms hot.
Cold state CZ1 and 365 ohms in parallel gives 208,63 ohms.
When hot the assembly turn to be a few dozen ohms.
I really don't know which shape this old CZ1 thermistor is. Anyway,
the total heater voltage raise smoothly up to 45 volts to 158vac, seems to be the most important.
Have a nice week end everybody!
Roger
note: the 365 ohms take lot of the current when in parallel with the CZ1, cause it get hot, so that is less stress on the CZ1 I think. For stronger surge limitor this resistor could have been useless.

[FERNSEH]

Hi Roger,
The Mullard VA1026 is 40mm long and 10mm diameter and is for use in 0.3amp heater chains.. The cold resistance is 1000ohms. No parallel resistor is required.
I can post it off to you.

DFWB.

[rogerdup]

That is very interesting ! Thank you David, I will try this .
By the way, and sorry to change the thread idea:
I put an EF184 in place of the EF80 v1a on the LV30 RF stage. Sensivity boosted, splendid picture and careful with the contrast !
No secret: EF80 gain 6,8mA/v and the EF184 15mA/v ! The LV30 like !
I will try to make the test later on also for v1b and v1c, but perhaps get in trouble because of too much gain with all those EF184 in place..
Of course I did'nt change the polarity keeping the one in place for EF80 (270ohms).
Anyway, if PYE had EF184 available at LV serie time, they did not need for build fringe receiver. But the EF184 was born in 1960..
Roger

[rogerdup]

Originally Posted by mark pirate

All sections apart from one were open, the replacement dropper was from a later Murphy set.
I never thought of rewinding it at the time, if I had not found the dropper I would have used a few of those metal clad resistors.

Hi again Mark.
I can rewind the resistor chain for you. You have just to buy 3 packs of 28ohms/meter resistive wire by Conrad uk. I have to know what is the main voltage to apply to the chain. That allows me to calculate the 98ohm space It is actually not 98 ohms for me ; I have 241vac and should have raised the value in this space to 124 ohms.
You will have to install a 220ohms type resistor same as the photo as example. Cause described in my previous message.
Roger

[rogerdup]

Hello everybody,
Having plenty of time, I choose to completely rebuild the main resistor of the LV30. Starting by cleaning the rod for the remaining traces of paint. The resistive wire I mentioned in my previous thread appear to be too thin for a long lasting work on this resistor. So, I make some tests with a much stronger 15,6 ohms/m you can find on Ebay.com from a Bulgarian supplier.
It is well supporting the heat.
I also ordered the 19,3 ohm/meter which can do the job I think, and test it in a next step. It can fill the old 365 and 98 ohms section.
The price of those wires is very chip and so is the shipment. I put a photo of the starting rewinding. Wait for the rest of the wire to come to finish.
I would be pleased to give more infos for those interested in that topic.
Have nice week-end !
Roger

[rogerdup]

Originally Posted by rogerdup

Hello everybody,
chip and so is the shipment.
Roger

I mean cheap..

[rogerdup]

Final achievement of restoring the LV30 resistor chain.
I carefully calculate the ohmic value of the various sections to get the average 155,6v across the heaters voltage.
The resistive wire is 0.18mm - 19,3 ohm/meter CuNi alloy (copper/nickel).
I am thinking of painting the rod with blue high temperature paint to get the original appearance, but wonder if this would affect a proper cooling of the wire.
have a good week everybody!
Roger