Help with A.P.T. Electronic Industries Ltd. 1HB300 Regulated P.S.U.

[NickG0HIK]

Hi,

I've obtained this power supply in the hope of using it as the basis of workshop H.T. PSU.

It is not regulating, it has an output of 125v with full mains supply, and varies as the input is adjusted, so it is not regulating.

It has an internal w/w pot which I presume sets the output volt but it does nothing.

GZ34 rectifier

3 off EL86 pass

ECC82 controlling element

Strangely there is one transistor a Silicon PNP 2S324, which had a broken collector wire, which I have manged to solder back on.

Any help with this or even better a circuit would be great.

Thankyou

[WME_bill]

APT stabilised power supplies. 1HB family.
I attach the manual for this family, from 1HB-150 to 1HB-300. The circuit attached is actually for the 1HB-150 model.
All models of the family will be similar, with different transformer output voltages and a few different resistor values for the regulating feed. A quick inspection of your unit will show you the differences.
Could you please let us know the circuit value changes for your model.
It is a fully regulating supply.
I suspect you will have to replace the silicon transistor; your soldering the lead back on hasn't worked. Almost any Si pnp low power, low voltage, general purpose will do, as the Brush OC468 or Texas 2S324 are both well obsolete.
wme_bill

[Silicon]

I repaired the power supply section of a Marconi TF144H which may be of similar age.

I had to replace nearly all of the carbon composition resistors and all paper capacitors to get it to work.

The valves were OK but the valve holder contacts were corroded.

[NickG0HIK]

Thanks for the manual, that should really help.

Yes I'll report back on how I get on.

I have checked the valves on my valve tester, I've also checked the resistors, they all seem to be near enough. I've checked the caps on a megohm range. But will also check them with a "Megger", which has found plenty of faulty caps in the past and helped me get several items of kit working again.

Nick

[NickG0HIK]

Thanks again for the circuit.

The culprit was R29 O/C.

Strangely, the circuit does not regulate immediately, the voltage rises as the valves warm up, the output voltage overshoots the setpoint and then settles down do the correct value, this overshoot is only for around one second.

I've not changed VT1, so it maybe worth trying.

I've not checked all the resistor values, but the ones I've checked are on the attached.
Other circuit changes around the pot I've drawn on.

Also four 100uF smoothing caps are used in a series parallel arrangement with 150k equalizing resistors.

I also shown the arrangement I've tried for a greater swing of output voltage.
Which ranges from 150v to 400v, I set the output to 250v, with no load, 100mA and 200mA load I could discern no change in voltage.

Now to find a project box and meter to make it a very useful addition to the workshop.

Nick

[Herald1360]

The overshoot could simply be down to differential heater warmup rates or the loop time constants. Once it's up and running, if you dial in a step change in output (well as steppy as a pot tweak can be), does the output overshoot before settling then. Does the behaviour vary between loaded and unloaded output states?

[turretslug]

Overshoot on the initial warm-up could also be the 85A1 reference needing a striking voltage somewhat above running voltage- ISTR, it's a rather early type of reference (as distinct from shunt stabiliser) with a striking voltage approaching 130V, so the initial output volts would be likely to climb somewhat before the reference fires and settles. They can be a bit variable in this respect and not helped by ageing- I've played around with gas reference circuits over the years and sometimes there can be a bit of "come on you , light up...." if you haven't allowed a good striking margin.

The little B7g 85A2 replaced the clunky B8b 85A1, it's plentiful and probably is more refined, ISTR striking volts may have been nearer 110 than 130V.

[WME_bill]

APT 1HB-300 power supply unit.
I am glad you have solved the failure to regulate with that faulty resistor.
I am rather doubtful about this popular policy of change all capacitors and all resistors before you find out what is wrong. Often the removal and resoldering creates more faults than the original.
I do suggest that the first step is to measure all voltages and try to understand what has failed. Yes, change the main electrolytics if they are obviously gone, but a slow bring up to voltage, using a series lamp or variac will often reform them enough to give you a good idea what else needs long term replacement.
Your overvoltage spike when starting seems due to different valve warmup times - I agree with Herald1360 and turrenslug.

Could I mention another point. This unit is designed to give a constant voltage output at varying current loads, your model at 300v at up to 175ma.
The input to the series dropper valves is at 600v. So they are dropping 300v and quite a bit of power. At 100ma say, power dissipation is 30watts.
I suspect you hope to make it give you fully variable output voltages. If you try to make it give you say 100v at the same current, then the power dissipation in those three EL86 will be 50W. Maximum dissipation of the three valves is 36W, so it will all get very hot.
wme_bill

[NickG0HIK]

Originally Posted by Herald1360

The overshoot could simply be down to differential heater warmup rates or the loop time constants. Once it's up and running, if you dial in a step change in output (well as steppy as a pot tweak can be), does the output overshoot before settling then. Does the behaviour vary between loaded and unloaded output states?

Yes, I think your correct, a quick wipe of the pot and it sets immediately.

[NickG0HIK]

Originally Posted by turretslug

Overshoot on the initial warm-up could also be the 85A1 reference needing a striking voltage somewhat above running voltage- ISTR, it's a rather early type of reference (as distinct from shunt stabiliser) with a striking voltage approaching 130V, so the initial output volts would be likely to climb somewhat before the reference fires and settles. They can be a bit variable in this respect and not helped by ageing- I've played around with gas reference circuits over the years and sometimes there can be a bit of "come on you , light up...." if you haven't allowed a good striking margin.

The little B7g 85A2 replaced the clunky B8b 85A1, it's plentiful and probably is more refined, ISTR striking volts may have been nearer 110 than 130V.

I've just tried an 85A2 and it's just the same.

[NickG0HIK]

Originally Posted by WME_bill

APT 1HB-300 power supply unit.
I am glad you have solved the failure to regulate with that faulty resistor.
I am rather doubtful about this popular policy of change all capacitors and all resistors before you find out what is wrong. Often the removal and resoldering creates more faults than the original.
I do suggest that the first step is to measure all voltages and try to understand what has failed. Yes, change the main electrolytics if they are obviously gone, but a slow bring up to voltage, using a series lamp or variac will often reform them enough to give you a good idea what else needs long term replacement.
Your overvoltage spike when starting seems due to different valve warmup times - I agree with Herald1360 and turrenslug.

Could I mention another point. This unit is designed to give a constant voltage output at varying current loads, your model at 300v at up to 175ma.
The input to the series dropper valves is at 600v. So they are dropping 300v and quite a bit of power. At 100ma say, power dissipation is 30watts.
I suspect you hope to make it give you fully variable output voltages. If you try to make it give you say 100v at the same current, then the power dissipation in those three EL86 will be 50W. Maximum dissipation of the three valves is 36W, so it will all get very hot.
wme_bill

Yes, but without a circuit diagram it is difficult, especially for folk without the experience. Sometimes a wholesale change of components can be the only way.
In this case once I had a circuit diagram it was pretty easy as it was one of the first voltage checks.

Yes, I'm aware of the reduced current to keep the valve within there rating, but luckily valves are pretty tolerant to overload especially short term.