EL3516 no sound

[DMcMahon]

Looking at your meter spec on AC voltage it is only spec'd up to 1,000Hz, i.e. 1 kHz

From your scope reading the bias frequency is around 40kHz so the meter will not be able to read the bias voltage accurately, if at all and possibly may load the bias signal
and could well explain why the scope voltage display drops to 140V.

If the meter had a frequency spec to be able to measure the 40kHz it would be an r.m.s. reading which of course is very different to the scope peak to peak reading.

David

This is ref Post # 39.

[ms660]

The 4mV figure at that test point will be the record signal voltage (RMS) for the quoted input and frequency which so far as I can make out is 0.55mV at 1kHz at the microphone socket.

The bias frequency voltage across the same test point with C12 set to max. is given as greater than 130mV at a quoted frequency of 41kHz to 48kHz, the peak to peak voltage of 130mV would be approx. 367mV.

EDIT: Post crossed.

Lawrence.

[Phantomrose1999]

Thank you david, good to know why my DVM was showing zero.

Thank you Lawrence, I will try adjusting C12. I have disconnected it and it measured 38pF.

Is such a high voltage across the head normal ? Never heard of it. My Grundig’s are around 24ish.

[DMcMahon]

Some recorders can have very high peak to peak bias voltages.

Try to see if by adjusting C12 you can get the level at M2 down to the stated 130mV (367mV p-p).

David

[Phantomrose1999]

Well it’s fixed. Big thanks to all who gave me quite a few lessons

Special thanks to Paula for all your detailed explanations

I adjusted c12 to bring the bias voltage across R21 to the required 368mV and it’s now working beautifully!

https://youtu.be/m2wbROsC49M


1st photo is the bias with no input across R21

2nd photo is it recording, across R21

[DMcMahon]

Great news, so looks like too large amplitude of record bias was the problem.

Only 1 photo above ?

Out of interest after C12 adjustment did you remeasure the amplitude of the bias across the record head ?

David

[Phantomrose1999]

I added two more measurements at the head.

1. Bias voltage at the head with no Audio 126V

2. Bias and 1khz audio at the head with magic eye close to maxed out

Hopefully this can help someone else.

[Phantomrose1999]

Last point. Trying to get a good rewind.

Should the 3 pads under the reel be smooth ?

Should the cork in the centre be oiled ? To help it slip a little ?

Thanks

[DMcMahon]

Originally Posted by Phantomrose1999

I added two more measurements at the head.

1. Bias voltage at the head with no Audio 126V

Your bias voltage signal without audio looks like there is an audio signal present, i.e. the +ve and -ve slopes of the sine wave should be clean/straight maybe it is just an artifact of the scope digital display/triggering etc.

David

[Phantomrose1999]

Originally Posted by DMcMahon

Your bias voltage signal without audio looks like there is an audio signal present, i.e. the +ve and -ve slopes of the sine wave should be clean/straight maybe it is just an artifact of the scope digital display/triggering etc.

David

It’s just the scope, if I blow it up, the bias is a perfect sine wave.

Been trying these polyurethane rubber belts, just heat the ends with a lighter and stick them together. Works very well indeed.

Last issue, there is a mechanical “rattle” sound and can’t find it. So annoying, maybe it’s the poly belt. Might try a 4mm instead of the 3mm.

[Phantomrose1999]

Test run. Still some crackling when recording. The tone and volume controls are not great

But it does work and goes into the shipping container. Ha

https://youtu.be/B-6HIs47wEI

Also got an AKAI M7 for $20 from the same guy. The amps work but can’t record. Needs a recap.

https://youtu.be/aRHbwA9G97U

[DMcMahon]

Originally Posted by Phantomrose1999

Last point. Trying to get a good rewind.

Should the 3 pads under the reel be smooth ?

Should the cork in the centre be oiled ? To help it slip a little ?

Thanks

See Post # 4 at this link for information on replacement pads.

https://www.google.com/url?client=in...Ak30xDvSxKZdqE

David

[Phantomrose1999]

Tks David. Good read in the link.

I was lucky the rubber pads and cork are in excellent condition. I just sanded the rubber pads and rewind is beautiful.

I oiled the cork friction pads, can’t find any reference to this being needed or not. When cleaned the friction was too much, so oiled them up and works fine

[Phantomrose1999]

Well, the joy of old stuff. A few noticed crackling and poping while turning the volume control. Well, got worse and playback was failing, with loud crackles. Noticed the magic eye was moving violently and it’s brightness was diming.

So must be a short. Tapping the ecc83 made it bad so resoldered the base, cleaned the contacts and even tried another valve. Put it all back together and no change

So next I tapped the EF86 and everything from going dead while playback to oscillations and strange noise. Ahah ! First removed it and tapping made no difference. Signal at middle of volume pot produced sound.

So swapped it out and finally playback is great. No pops or crackles.

So valves do fail ! Only my second. Other was an ecc83 not drawing any power.