Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

[Kanyehobbitkind]

Hey guys.

Now I will apologise, as I'm not the most knowledgeable when it comes to vintage audio devices, which is why I've turned to this forum for help.
I've recently acquired my Grandfather's vintage radiogram which I'm hoping can be restored. The table itself has a Dynatron SRX25 radio with a Garrard 40B turntable. When I got the table the power cord was cut, as my grandfather didn't use it anymore, so I was a bit confident about being able to restore it (in hindsight I was a bit naive).

However I got a new power cord all sorted and soldered onto it nicely, turned the switch and the power came on, I was so happy the Garrard 40B spun and everything! the only issue was there were no speakers with it, and to be honest I don't even have a clue what the original output for the radiogram is, but I got a 2 pin Din adaptor which apparently is for the correct one, plugged some speakers in it and nothing at all came out.

Now I have access to an Oscilloscope at work and through the headphone and speaker outputs nothing at all. I've replaced all the fuses and I'm completely stuck on what the issue could be. I can't find any schematics for it, but I've seen that the transistors were 'Newmarket' brand and can't find any anywhere at all.

I have pictures attached but in the hopes there's something quite simple in there anyone can see.
If I could I'd just purchase a new SRX25, but I also can't find them anywhere either which is a bit of a nuisance.

Anyway any help at all would be appreciated on how I could restore this beautiful Radiogram.

Thank you
Kane

[paulsherwin]

Newmarket transistors were made by Pye, who also owned Dynatron at the time. You're unlikely to find them now, but there's no reason to think any transistors are bad at this stage.

The fact that it's completely silent is actually good news, as most faults will affect one of the stereo channels and not the other. Can you check your speaker connections, as it doesn't sound as if you are too confident about that? What speakers are you using? A DIN speaker plug has a pin with a spade contact above it. What is your 'adaptor'?

If there is a headphone socket, have you tried using it?

If there really is no output, you need to look at the power supply arrangements. Is anything lighting up when you switch on?

[Michael Maurice]

First things first. Use a meter with one probe connected to chassis and with the other measure the voltage on the four output transistors at the back. This is a positive earth chassis so readings will be negative. two transistors should read -30V approx the other two should read -15V

Take those readings and report back.

[Kanyehobbitkind]

Originally Posted by paulsherwin

If there is a headphone socket, have you tried using it?
If there really is no output, you need to look at the power supply arrangements. Is anything lighting up when you switch on?

I soldered the speakers together myself from old speakers I had that worked, once I soldered them I tested them and they did work, but when plugged into the sockets no sound at all, not even white noise. The same happened when I plugged headphones in (actually took me longer than I'd like to admit to figure out they were headphone jack as it honestly looked like something you'd screw the aerial into as it was on the back not on the Radio itself haha). The radio and everything lit up once I turned the power on, the light in the bottom left corner turned on too so power is there. I've uploaded a picture of the adaptor now to show you which ones they are.

Would any transistors work for it as I thought these were odd ones?

Thank you
Kane

Originally Posted by Michael Maurice

Take those readings and report back.

Would this be any part of the Chassis or a specific part?
Sorry I'm just a little new to using all of this equipment and I'd prefer to not mess it up and end up damaging the radiogram haha.

Thank you
Kane

[Nuvistor]

Srx25 info, not the makers manual but better than nothing.

http://www.service-data.com/product....21/1826/a11321

[Station X]

Check the three fuses visually to check they haven't blown.

Then measure the DC voltage with respect to chassis on both ends of the two fuses feeding the two channels of the amplifier. NOT THE MAINS FUSE.

[Kanyehobbitkind]

Originally Posted by Station X

Check the three fuses visually to check they haven't blown.

Then measure the DC voltage with respect to chassis on both ends of the two fuses feeding the two channels of the amplifier. NOT THE MAINS FUSE.

I replaced the 3 fuses just to ensure that they'd work, however how would I measure the DC voltage correctly? (I don't want to mess anything up and damage the table as I'm quite new to this)

Thank you
Kane

Originally Posted by Nuvistor

Srx25 info, not the makers manual but better than nothing.
http://www.service-data.com/product....21/1826/a11321

That's awesome thank you,

Kane

[Michael Maurice]

You need a multimeter, you need to know how to use it, switch the multimeter to volts and with the black probe connected to ground or chassis, use the other probe to make make the readings.

[Station X]

Originally Posted by Kanyehobbitkind

I replaced the 3 fuses just to ensure that they'd work, however how would I measure the DC voltage correctly? (I don't want to mess anything up and damage the table as I'm quite new to this)

Thank you
Kane

Set you meter to measure DC Volts and set it to the highest voltage range.

Make sure the leads are plugged into the correct sockets on the meter. Generally marked as COM for the black lead and Volts/Ohms for the red lead.

Clip the red lead to the chassis. Probe the fuses with the black lead. You'll have to switch down the ranges to get a sensible reading.

I've suggested connecting the red lead to chassis in case you have an analogue meter.

[Michael Maurice]

These transistor must be replaced with the same types, you can't really use equivalents, they don't work well, believe me I know, I've tried it.

['LIVEWIRE?']

THose adaptors in post # 4 are DIN Speaker Plug to Phono (RCA) Sockets, so should only be used if the speaker leads are fitted with phono plugs. Ideally, your speaker leads should be terminated with DIN Speaker plugs, one wire of each speaker lead going to the centre (Flat)pin, and the other to the round pin. A seperate speaker should be connected to each channel (output) socket of the stereo. Using those adaptors, Kanyehobbitkind, how did you connect the wires from your speakers to them?

[Kanyehobbitkind]

I connected them through Phono speakers, the flat pin in the centre and the circle connected to the top, I would've got the correct speakers for it but couldn't find them anywhere at all so I thought I'd be able to use Phono's until I got the table up and running then eventually get some correct Dynatron speakers when I could find some.

Thank you
Kane

[Kanyehobbitkind]

Originally Posted by Station X

Set you meter to measure DC Volts and set it to the highest voltage range.

Make sure the leads are plugged into the correct sockets on the meter. Generally marked as COM for the black lead and Volts/Ohms for the red lead.

Clip the red lead to the chassis. Probe the fuses with the black lead. You'll have to switch down the ranges to get a sensible reading.

I've suggested connecting the red lead to chassis in case you have an analogue meter.

That's awesome thank you!
I'm in work tomorrow so can use the multimeter then, however I'm not too sure about why the fuses if I've replaced them, is it to ensure that the correct volts are travelling through them and if it's not then there's an issue before we get to the fuses?

Thank you
Kane

[Kanyehobbitkind]

Originally Posted by Michael Maurice

These transistor must be replaced with the same types, you can't really use equivalents, they don't work well, believe me I know, I've tried it.

That's what I was thinking, but Newmarket aren't around anymore so if it is them does that mean I'm totally out of luck?

Thank you
Kane

[paulsherwin]

First of all, there's no reason to expect you will need to change any transistors. The complete lack of output is very unlikely to be caused by a transistor fault.

If you really do have some bad transistors, they can be replaced with new old stock parts, or different substitutes fitted. This isn't always straightforward but it can be done. It's not a job for a beginner though, as some circuit modifications may be needed.

If the worst comes to the worst, the entire power amp circuitry can be replaced by modern power ICs. The parts for this are pretty cheap, though obviously there's expensive labour involved if you can't do the work yourself.

[Kanyehobbitkind]

Originally Posted by paulsherwin

First of all, there's no reason to expect you will need to change any transistors. The complete lack of output is very unlikely to be caused by a transistor fault.

If you really do have some bad transistors, they can be replaced with new old stock parts, or different substitutes fitted. This isn't always straightforward but it can be done. It's not a job for a beginner though, as some circuit modifications may be needed.

If the worst comes to the worst, the entire power amp circuitry can be replaced by modern power ICs. The parts for this are pretty cheap, though obviously there's expensive labour involved if you can't do the work yourself.

Is there anywhere I'd be able to find the new old stock parts? (sorry I'm not actually 100% on what that means).

I can repair motherboards and solder, transistors I've never done to this extent but I'd get some test ones before I actually worked on the Dynatron one just to ensure I can do it properly.

Thank you
Kane

[Station X]

Originally Posted by Kanyehobbitkind

That's awesome thank you!
I'm in work tomorrow so can use the multimeter then, however I'm not too sure about why the fuses if I've replaced them, is it to ensure that the correct volts are travvelling through them and if it's not then there's an issue before we get to the fuses?

Thank you
Kane

Yes. The voltage check is to check that voltage is actually present at the fuses. This will show whether or not amp's power supply is working correctly.

Don't concern yourself with sourcing new transistors at this stage. They may not be needed. Under no circumstances change components because you "think" they may be faulty.

[paulsherwin]

New old stock parts (NOS) are new parts that have sat in a warehouse or workshop for 50 years. As Graham says, don't worry about this at this stage, and never change random parts in the vague hope of curing a fault.

[Edward Huggins]

To help us to help you better, when you use the word "Table" do you really mean the Turntable or the complete Dynatron Unit?
Also you say "Phono Speakers", do you mean speakers that have a Phono plug at the end of the connecting cable rather than a DIN plug?

[Michael Maurice]

Before worrying about fitting parts, you MUST do the checks on the O/P transistors as I suggested in post 3.

These readings tell me a lot and I can guide you through it when you tell me what you get.

Regards

Michael