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A.P.T valve stabilised PSU

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PYE625
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Hi all,

My next project will be this power supply I have just bought for £80 on ebay. (It was £100 originally). Bearing in mind that a good Mullard GZ34 rectifier can fetch this figure alone, I thought it was a reasonable price with free postage too.

It caught my interest as it is a valve stabilised PSU and will be useful for me playing with valve amplifiers etc.

Judging that it seems to have three EL86 series pass output valves, I am guessing it is able to provide a likely output of 250-300vdc upto 150mA. There is also an ECC83, 81 and an 85A2 voltage stabiliser.

It was made by a company called A.P.T in Surrey and I would guess it dates from the mid 60's.

Here are the vendor's photo's for now....

s-l1600.jpgs-l1600-1.jpgs-l1600-2.jpgs-l1600-3.jpgs-l1600-4.jpg

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 08/11/2017 6:08 pm
crustytv
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Very nice Andrew and very useful, look forward to it on your bench and the reports.

I have a much more modern affair, weighs an absolute tonne. A Claude Lyon Voltage stabiliser. They sound grand but its basically a motorised variac that maintains a steady state voltage that the user sets. I bought mine to supply my valve tester with the steady state supply. No point trying to test valves with a fluctuating mains input the suppliers deliver us, skews all the readings. Hardly gets used now as I hardly ever test valves anymore.

clyon.jpg

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Posted : 08/11/2017 6:36 pm
Marc
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Hi Andrew,

That's quite some hefty beast for 150mA isn't it.

Good grief ! Are GZ34's really fetching that sort of money eek_gif

Marc.

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Posted : 08/11/2017 6:36 pm
crustytv
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Marc said
Good grief ! Are GZ34's really fetching that sort of money eek_gif

Marc.  

Yes and have been for some years now. My first valve tester had its one stolen when I bought it. nuts_gif I had to slap two silicons as the glass was waayyy too expensive.

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Posted : 08/11/2017 6:41 pm
PYE625
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A Mullard or Philips GZ34 can be rather pricey to say the least, especially if it has a metal band around the base. For some reason, these must be so much better. I'd love to know why duno_gif

Have a gander on ebay, you'll soon see what I mean about the prices. wink

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 08/11/2017 6:49 pm
Marc
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PYE625 said

Have a gander on ebay, you'll soon see what I mean about the prices. wink  

I just have..... just picking my jaw back up ! eek_gif

Mind you there are some equivalents for just over a tenner. wink

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Posted : 08/11/2017 7:05 pm
PYE625
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Marc said

Mind you there are some equivalents for just over a tenner. wink  

Correct, and they are just as good except for perhaps the most demanding of applications.

As for the PSU, I will try and find some data on it, but until I can see the model number there is little chance. Even knowing the model anyway, it could be difficult.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 08/11/2017 7:47 pm
PYE625
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Chris said
Very nice Andrew and very useful, look forward to it on your bench and the reports.
  

Speaking of benches, I have just bought a used one locally and am collecting it Friday. It is 80cm deep and will be better for TV set's than the 60cm I have at the moment. (I'll put some pic's later in my "new workshop" thread.)

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 08/11/2017 7:56 pm
Nuvistor
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https://www.radiomuseum.org/dsp_hersteller_detail.cfm?company_id=15204

 

Just some company information, no circuit. 

There are some valve regulator designs in WW  or the Practical Wirelss/TV, probably very similar. Worth a search.

Frank

 
Posted : 08/11/2017 8:00 pm
PYE625
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Thanks Frank,

Reading the info could mean that the PSU was made just prior to 1960, on account of the company moving to Reading in that year and the PSU label stating "Byfleet, Surrey".

That's a bit confusing.... Am I reading in Reading, or Reading in reading ?  grin_gif

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 08/11/2017 8:06 pm
PYE625
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Hi all, the PSU arrived safely and well packed today and the model is IVC 250. (Nothing on Google about it that I can find).

Once I have some bench time, I'll have a look at it 🙂

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 13/11/2017 5:40 pm
PYE625
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As usual, I couldn't wait, and had more than a quick peek.

The transformer is ok, the main smoothing caps are 4x 100uf 450v and are reading nicely between 99 and 104 uf. They are being re-formed at the moment. I applied mains, all valves in place except the GZ34 rectifier which is fine fortunately, and checked the AC voltages. All ok heater voltage wise and the HT secondary is approximately 320-0-320 vrms. So good, so far.  🙂

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 13/11/2017 10:04 pm
Nuvistor
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This is just going to work, especially with the slow warm up you are giving it.

 

Frank

 
Posted : 13/11/2017 10:14 pm
Marc
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Posted by: PYE625

As usual, I couldn't wait, and had more than a quick peek.

I would expect nothing less from you  😉

Marc.

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Posted : 13/11/2017 10:15 pm
PYE625
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This evening I have been sketching out the circuit. One odd thing for me is that two 100uf 450v capacitors are wired in series for main smoothing and again on the set output voltage. From what I can see, HT is not going to be much greater than 375 volts at most, so what the point of this is, I have no idea.

Here is my attempt at circuit drawing.... On paper it looked ok, but now on here it's hard to read so I will re-draw it sometime.  🙂

 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 14/11/2017 8:25 pm
PYE625
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Some pics of the capacitors being reformed en-mass and of the unit itself.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 14/11/2017 8:27 pm
Nuvistor
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Presume they have used two to reduce the amount of heat in each on for long term reliability. 60uf is the max reservoir cap for a GZ34 so that will be the reason for them using 100uf.

Its also possible that in the design stage that found some anomaly and decided this was an easy way around it.

It not a consumer item so perhaps they built it a bit better.

All guess work as usual on my part.

Frank

 
Posted : 14/11/2017 9:07 pm
PYE625
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Thanks Frank, whatever the reason is I won't be changing the design. There are some large green wire-wound resistors marked APT and have custom values eg. 10.4 k, 17k, 8.75k and a 5.63k. They are marked as 1 %. Fortunately, these are ok. There are some bog standard carbon resistors too, and the values are out of spec on some so they will be replaced....namely the 150k's across the 100uf capacitors.

The electrolytics have reformed very well and the unit is now working, but one or two resistors and paper capacitors will need to be replaced. (I have replaced the valves that were broken, 1x EL86 and an ECC83).

PS....I have spotted at least one error in my circuit above, so please don't treat it as gospel.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 14/11/2017 9:40 pm
PYE625
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In re-forming the electrolytic capacitors pictured above, I cheated and split off the HT through four individual 27k resistors for each capacitor. This way, I was able to do them all at once. I achieved a HT source of 380vdc in a slightly naughty way, I used the 320v output from my capacitor reformer in series with an additional isolated 60v psu. The reason for this was to get nearer to the 450v rating of the capacitors. Whether I really needed to do this, I don't know, would 320v have been sufficient to properly reform 450v capacitors?

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 14/11/2017 10:30 pm
Nuvistor
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Who knows, at the price of GZ34 I think you need to do everything to protect the one you have.

I didn’t realise they were selling for that money.

 

Frank

 
Posted : 14/11/2017 10:45 pm
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