Thorn 1400 VDRs

BRC/Thorn 1400 employ 4 VDR's in its circuits as detailed below:-

• Z1

Type= 37P/W/Spec886
Function = UHF Tuner supply Stabilising
[/*:m:w0bz6e0c]

• Z2

Type=MU01
Function= Boost HT Stabilising
[/*:m:w0bz6e0c]

• Z3

Type=MU01
Function= Frame Output Transformer Stabilising
[/*:m:w0bz6e0c]

• Z4

Type=MU01
Function= Width Stabilising[/*:m:w0bz6e0c][/list:u:w0bz6e0c]

I would think its Z2 not Z1 that's giving you trouble.

CrustyTV Television Shop: Take a virtual tour
Crusty's TV/VCR Collection: View my collection
Crustys Youtube Channel: My stuff
Crusty's 70s Lounge: Take a peek

 

If your boosted HT is not stabilised as you describe in post #1, then as I say it will be Z2 not Z1. If so then I have just checked my stock and I have a couple of MU01 in stock, I can spare you one.

Let me know what you need Z1 or Z2

Once you're sure PM me your address and I will send one off to you.

Sorry for the confusion. I'll check in the morning but I'm sure you are right Crusty.
Thank for the offer I'll pm you tomorrow. That really is very kind of you.

Thanks again.
Would there be any modern equivalents.?

Sorry sorry sorry! They were 1500 chassis

Please see attached pictures.

Boost HT was around 420v with Z3 in circuit.
Removed z3 then boosted HT went up to almost 700.
This brought the picture up but with no width control working.

Sorry again for miss information, it's been a busy week!

Hi Rob,

No problem.

Regardless of the chassis mix up you will be pleased to know Thorn used the same width stabilising VDR in the 1400 & 1500, namely an MU01, so the offer still stands.

Chris

From the point of view of long term availability of these VDRs, I don't know if any data is easily available but I wonder if there is an alternative?

By comparing the circuitry of contemporaries of these Thorn chassis it should be possible to find (virtually) identical circuitry using Mullard/Philips VDRs which, due their international use in Europe in particular, would suggest that supplies of these VDRs might be easier to find.

Hi,

Usual voltage dependant resistor used in this position is type E298ZZ/05 listed in the Mullard Passive Components - Quick reference guide dated 1973 - 74 with brief data as follows...

Code number 564 90004
C (approx) = 3020
β = 0.16 to 0.21
Reference current = 2mA
Reference voltage = 950V
Diameter = 7.2mm
Length = 16.5mm
Maximum temperature = 150°C
Maximum dissipation = 700mW
Tag ended

Relationship between applied voltage and current flowing is given by:

E = CI^β (superscript representation not allowed for β)

Where E = volts, I = reference current , C is the reference voltage
β = slope of the characteristic.

Rich

Simply stated, the resistance of a VDR decreases as the voltage across it increases and follows a logarithmic function. Plotting current between 0.1 and 10mA and voltage across VDR according to formula on a log/log scale, the resistance can be shown to decrease.

It might be possible to test the voltage at a specific current, assuming a high enough voltage supply. As these devices are rated at a maximum of 700mW, the following graph (red plot) shows the limits of operation. Choose test values that does not exceed VDR dissipation. Monitor both voltage and current as supply voltage is adjusted. All this needs to be verified with an actual device!

Note: graphs are based on the relationship log V = β log I + log C .
Cheers
Rich

Thanks all for the info.
I do now have a replacement thanks to Chris
I will however, have a play and see if I can find something that might work as well, if the source of genuine VDRs drys up.

Cheers
Rob