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Old 8th Oct 2019, 7:55 am   #1
ahankinson
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Default Solartron SRS153 information

I am looking for any information, particularly a schematic, about the Solartron SRS153 HT power supply. I recently purchased one, and I can't seem to find any data that matches what I have in my hands. As far as I can tell, this doesn't match the SRS153.2 variant, which are the only schematics I could find.

The one I have has a single rectifier (A 5AR4) and two 12E1s. These might be substitutes for a different valve, though, since it looks like the top cap wire may be a later addition.

Any help or pointers to things I have missed would be greatly appreciated!
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Old 8th Oct 2019, 9:51 am   #2
Alistair D
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Default Re: Solartron SRS153 information

I think this is what you are looking for. The rest of the thread may also be of interest.

http://golbornevintageradio.co.uk/fo...d.php?tid=4760

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Old 8th Oct 2019, 10:05 am   #3
ahankinson
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Default Re: Solartron SRS153 information

Thanks Al! Unfortunately that's the schematic for the SRS 153 S, which I think was a higher-power variant.
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Old 8th Oct 2019, 9:05 pm   #4
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Default Re: Solartron SRS153 information

Here are some photos for reference. As you can see, there's only three valves, unlike the other schematics that seem to have 4 or 5. Looking at it again I am convinced that the top cap connection is a later addition (orange wire), but not much else seems to be changed.
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Old 8th Oct 2019, 9:24 pm   #5
M0FYA Andy
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Default Re: Solartron SRS153 information

That does look quite different, I've only come across the SRS153S, I have a couple of examples.

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Old 8th Oct 2019, 10:45 pm   #6
ahankinson
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Default Re: Solartron SRS153 information

It would be great to know what the original power valves were. The anode connection is bare wire and uncomfortably close to the top of the chassis, so I'd like to get that sorted out.
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Old 8th Oct 2019, 11:31 pm   #7
Alistair D
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Default Re: Solartron SRS153 information

I recognise your PSU from the fact that there are 2 internal pots for adjusting the voltage range. I had one that was very similar internally, alas I gave it away many years ago. As far as I remember the series pass valves were KT66s. What ever they were they did not have top caps.

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Old 9th Oct 2019, 6:38 am   #8
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Default Re: Solartron SRS153 information

Would have thought any beefy valve would do for the series pass valves, two EL34's would be cheapest but might need some alteration to the circuit.

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Old 10th Oct 2019, 1:04 am   #9
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Question Re: Solartron SRS153 information

In the photos, I see three valves. The smaller valve must be the twin anode rectifier. But how is the stabilization achieved? Usually, there is a neon-type valve for that - such as a VR150/30 (a.k.a. 0D3), an OB2 or an OA2. But I don't see one. There has to be some sort of reference voltage in the design somewhere, no?
Plus, are the two 12E1 valves wired in parallel, or is one acting as the error amplifier?

Just curious.

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Old 10th Oct 2019, 8:18 am   #10
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Default Re: Solartron SRS153 information

All good questions! Unfortunately without a schematic, I can't really tell you. I haven't had a chance to trace the circuit yet, so you know as much as I do at the moment.

I've also noticed that someone's bunged two diodes in there, which I suspect isn't original either, so it may be that they're trying to bypass the rectifier valve. They look to be in a strange place, however, hanging off the voltage range pots, so I'm not so sure.
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Old 10th Oct 2019, 1:13 pm   #11
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Default Re: Solartron SRS153 information

The SRS153 range are Variable voltage power supplies, not Stabilized power supplies.
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Old 10th Oct 2019, 1:22 pm   #12
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Default Re: Solartron SRS153 information

The SRS153S uses a half wave thermionic diode to create a negative supply which is connected to one end of the voltage potentiometer.

It probably allows the circuit to output voltages closer to zero than it would normally be capable of.
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Old 10th Oct 2019, 5:24 pm   #13
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Default Re: Solartron SRS153 information

Thanks, Silicon. Do you think some bright spark might have put in the SS diodes to bypass the valve?

I'm going to see if I can get a start at tracing the circuit tonight.
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Old 10th Oct 2019, 9:08 pm   #14
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Default Re: Solartron SRS153 information

I think your version originally had a metal rectifier for the negative bias.
The type made from a stack of metal discs.

It was mounted on the metal brackets near the potentiometer.
They are often replaced by silicon rectifiers when they fail.

The circuit may have been similar to the SRS153S version.

The SRS153S uses CV428 (5B/254M) valves which require a B8B valve holder.

Your Octal valve holders look original. The quality inspector may have put dabs of paint on the solder joints.
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Old 10th Oct 2019, 10:18 pm   #15
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Default Re: Solartron SRS153 information

Studying the pictures, the Octal valve holders are wired in the usual pin configuration used by the many output pentodes / tetrodes that followed on from the 6V6 and 6L6, including the KT66 and EL34. The top cap connections have been added by wiring to the anode pins on the valve bases, the 12E1 connections being otherwise the same.

The two valves are definitely wired in parallel.

I have the later version, labelled SR153.2. It uses a pair of 5B254M valves, often referred to as "miniature 807's", and three EY84 rectifiers - two for the HT and one for the negative bias. There is only one internal trimpot so there have been a few changes from the original SR153.

As mentioned above these supplies are variable, but not regulated or stabilised. It can be useful to have the entire range available on one turn of the pot, unlike the E350 and many other regulated supplies.
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Old 10th Oct 2019, 10:36 pm   #16
Silicon
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Default Re: Solartron SRS153 information

The wires going to the top caps of the 12E1 valves may have been replaced because they touched the hot valves and the insulation melted.

A good upgrade would be to replace them with high temperature silicon rubber insulated wires.

The HT on the smoothing capacitors will be about 600V DC. Take care!
Not many valves are suitable for that voltage.

If the 12E1s are not original but the valve holders are, the only likely alternative is the 6146 beam tetrode which has an Octal base.
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Old 12th Oct 2019, 5:46 pm   #17
ahankinson
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Default Re: Solartron SRS153 information

I've gotten around to tracing the circuit, and have attached it for reference. I've also double-checked with the schematics from the latest variants and there are some similarities. Component numbers on my schematic are roughly equivalent, where possible, to the later schematics (Specifically, the .S variant schematic linked above).

On the way I've found that it's not really a happy camper. Some charring on wires indicates that something is off. I've measured component values as best I could but did not take anything out of circuit to measure them. Not all components measured healthy. (I haven't plugged it in yet, and don't intend to until the issues have been addressed and the wiring re-done)

I'm not familiar with the resistor code colouring scheme for two of the three wire-wound resistors. I've looked them up and I *think* they're supposed to be 470kΩ ("Yellow") and 330kΩ ("Orange"). Could someone confirm that?

There is some strangeness for the grid resistors (pin 5). V2 has a 10kΩ (Br. Bk. Or.) while V3 has 100Ω (Br. Bk. Br.) in the same position. Both *look* factory, but the one on V2 could be a later addition.

I would appreciate any feedback. I'm sure there are not a few errors in this, so a second (or third or fourth!) pair of eyes would go a long way towards untangling this.

Edit: In fact, just after I posted this I realized that I had the connection between the heaters and the cathodes wrong. I've fixed that and re-uploaded a new version.
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Last edited by ahankinson; 12th Oct 2019 at 6:04 pm.
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Old 12th Oct 2019, 5:49 pm   #18
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Default Re: Solartron SRS153 information

I should also add that without a transformer diagram I'm flying a bit blind for winding layouts. Instead, I just used the numbers on the pins.
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Old 12th Oct 2019, 6:30 pm   #19
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Default Re: Solartron SRS153 information

The large carbon rod resistors use the 'Body - Tip - Spot' paint code.

The 330kOhm one seems OK. If there is no extra spot on the other resistor, it should be 470kOhms.

You could check the all valves individually for continuity across all combinations of valve pins to see if there are any heater - cathode shorts, etc.

Test it in stages. Make sure the metal case has continuity with the mains plug earth pin.
Remove all valves and test transformer generally. Power up using a lamp limiter.
Measure negative bias voltage.

Then add the rectifier and test the HT voltage across C1.

Then add one 12E1 valve, set voltage knob half way, turn on and check various voltages.

Ideally you don't want to be using test lead probes on a high voltage device like this.
I attach meter leads fitted with insulated croc clips to the circuit and then turn the device on.
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Old 12th Oct 2019, 7:05 pm   #20
ahankinson
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Default Re: Solartron SRS153 information

Thanks, Silicon. Yes, I am paranoid about not touching HT circuits when they are active.

Clip leads, step back, switch on, make measurement, switch off, remove leads. And still keep one hand in my pocket!

I'm not going to power anything up until after I've done a thorough check of the wires and replacements. I'm going to put 600v silicone hookup wire throughout, except for the mains and heater connections which will get higher-rated cables.
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