Capacitor advice please for FERROGRAPH 632

[DOFFERY]

If you have not checked for the erase voltage which would at least ascertain the condition of the head, I think you should sit down & start again . Forget the caps. that seem to worry you , your osc. would appear to be in good condition, the bias also would seem to be OK, just erase at fault.. Now where would you start , first If erase voltage OK post 20 above plus other connections (many plugs/sockets) would appear to be your next choice.

We all get lost at times & I have found a rest from the problem helps, then start from the beginning, you know the erase is the problem, hence !!!!

Colin.

[Nightcruiser]

Firstly I'd like to thank everyone who has helped with advice this week on this particular problem.

The switch is next to check through. I've cleaned it thoroughly enough with servisol but until I get a meter on it that is no absolute guarantee. If the head has gone open circuit that is another matter but I think it's unlikely. The erase head on this machine is of a strange looking brass construction though unlike the other Ferro's I've previously owned.

I'll try to get a pic of it uploaded over the next day or two and attempt to do some readings for o/c.

[Nightcruiser]

I've checked the voltages at the head and they are minimal 3-4 volts...nowhere near 27-30v that was expected.

[DOFFERY]

Is the erase low on individual tracks but OK on stereo, ie nearer the normal voltage ?

As you state you can record OK, it would again point to the erase head (both tracks being U/S is unusual )or more likely the various switch / plug socket connections, as mentioned in a previous post assuming all else is correct .

What is the bias voltage on the R/P head, OK on individual tracks & stereo?

Colin.

[Nightcruiser]

If I am measuring the correct pins, I am getting 32volts on one side but very low (3v)from the other pair. This is in the stereo position.

The actual recording is fine. No problem there. No distortion.

When attempting to erase the previous recording without an input source it is still very weak and what was previously recorded is easily recognised.

When I switch to either upper or lower track while recording there is no erase at all and it is just as if I am playing back the tape

Also If I turn from the stereo position to the upper position while making a recording or attempting to erase without source the oscillator will record a increasing in pitch signal onto the tape which sounds rather like a flashgun charging up.

[Nightcruiser]

Using a new fresh blank tape I recorded an audio source in the stereo position

Rewound the good recording then attempted to erase without input source and turned track selector throughout the various positions while the machine was running and got the following results when I replayed the tape

Upper track poor erase...25%

Switch to stereo it is better....50% erasure quality but still not anywhere near perfect

lower track hardly any erasure whatsoever - marginal difference if anything noticeable

[DOFFERY]

Still points to switching problems or the erase head , faulty on one track. Have you measured the resistance on the erase head tracks?
Just to confirm
erase 27/30 volts.
record 14/20 volts.

Colin.

[Phil G4SPZ]

The fact that the voltage is low across one of the erase head's two tracks points more to a fault upstream, rather than in the head itself.

As an alternative to measuring the head's resistance using DC and thus risking magnetising the head, what about inserting temporarily a resistor in series then checking the oscillator voltages appearing across head and resistor? If both are low, the fault is upstream of the head, whereas if the voltage across the head is high or very low, the head is open circuit or short circuit respectively.

You also mentioned that the oscillator signal could be heard 'winding up' from low to high, which points to a fault in the oscillator itself - the frequency should be above the audible range.

Originally Posted by ricard

but be sure to demagnetize the head afterwords before running any tape through the machine.

Surly the erase power would do this anyway.

[SteveCG]

I have not dealt directly with a 632, but being a valve model, have you checked all the paper capacitors for leakage? I had a Ferrograph series 2 where all the paper capacitors were significantly leaky - including the 0.5 micro-F bias capacitor - and needed replacing.

[DOFFERY]

Hi John,
Received your email, when I locate the item I am looking for, will advise asap.

Colin.

[DOFFERY]

contact me John, have the details ready.

Colin.

[ricard]

Originally Posted by merlinmaxwell

Surly the erase power would do this anyway.

Yes it should, but that assumes that you actually remember to switch the machine to record after measuring the erase head before starting the machine with tape afterwards. I just think it's easier to remember to always demagnetize a head after a DC current check.

[DOFFERY]

This thread has been resolved so I think it should be closed.

Colin.

[llama]

Can we hear what the solution was, please?
Graham

[DOFFERY]

As requested, the last problem was a fault in the connecting cable .

Colin.