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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 25th Oct 2020, 7:19 pm   #21
ms660
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Default Re: Ferrograph Quiet Crackly Audio

The most common failure mode for sufflex capacitors is open circuit or very high ESR, I don't think I have had more than half dozen go short circuit in my years in the trade.

Hopefully the HT check will tell which way to go.

Lawrence.
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Old 26th Oct 2020, 12:33 am   #22
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Default Re: Ferrograph Quiet Crackly Audio

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Originally Posted by barrymagrec View Post
Check voltages before you change any more caps - you have two faults which could both be HT volts.

Suflex caps rarely fail unless damaged by a careless soldering iron.
Yeah I do want to try and avoid touching those caps if I can since I know polystryenes are easily damaged with heat.
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Old 26th Oct 2020, 8:44 pm   #23
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Default Re: Ferrograph Quiet Crackly Audio

Alright, heres what i've been able to measure.

I measured between the valve pin and ground with the exception of the EZ80 anode which was measured between the anode and centre tap of the transformer so its in range of my meter.

V7 (EZ80):
Cathode: 298vdc
heater: 4.9ac
Anode (a): 283ac (to centre tap)
Anode (a"): 283ac (to centre tap)

V6 (ECC82):
Anode (a"): 0v (tested for both ac and dc. nothing at all)
heater: 3.3vac
Anode(a): 0v
Grid(g") 0.34vdc
Grid(g) 0.33vdc

The voltages on the EZ80 seem okay to me.

Looks like it could be something in the oscillator circuit. It's unlikely to be the valve itself since its a NOS phillips but I wont rule that out. I'm getting some more valves in stock soon and one of them is indeed an Ecc82. Might try substituting them.

I'm a little worried about testing the grid coupling capacitors because of their fragility.

Its also worth pointing out that the anode voltages of the EZ80 went up to around 350v but then started to drop and then rested at 298. I'm assuming thats normal as the other valves start to warm up and thus introduce a load?

Any ideas on where to go from here?

** machine was in record mode when testing
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Old 26th Oct 2020, 8:52 pm   #24
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Default Re: Ferrograph Quiet Crackly Audio

You won`t get a sensible reading on V6 unless the selector switch is in the record position.

Check R2.
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Old 26th Oct 2020, 8:55 pm   #25
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Default Re: Ferrograph Quiet Crackly Audio

What about the anode of V5 (ECC83) the anode that's connected to pin 7 of SK1?

Lawrence.
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Old 26th Oct 2020, 9:03 pm   #26
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Default Re: Ferrograph Quiet Crackly Audio

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You won`t get a sensible reading on V6 unless the selector switch is in the record position.

Check R2.
The machine was in the record position. Hence I think it's a little odd.

Quote:
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What about the anode of V5 (ECC83) the anode that's connected to pin 7 of SK1?
I'm going to check the amp voltages tomorrow most likely since to be honest i'm rather tired this evening and that's a bad thing around high voltages. I'll update the thread when I do.
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Old 26th Oct 2020, 9:11 pm   #27
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Default Re: Ferrograph Quiet Crackly Audio

You appear to have no HT on the oscillator valve - this would explain no erase. You`ll have to chase it through the sockets and the switch.
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Old 26th Oct 2020, 9:20 pm   #28
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Default Re: Ferrograph Quiet Crackly Audio

That would make sense. Which sockets and switches would I be looking at exactly? As far as I can see the only sockets that are connected to the oscillator are SK8 and SK9 which are used to enable or disable erase / bias.

I checked these earlier. One of them isnt in the best shape but I tested them for continuity and its fine despite appearance. I did also try swapping them but no change. I'll go back and double check them anyway.
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Old 26th Oct 2020, 9:30 pm   #29
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Default Re: Ferrograph Quiet Crackly Audio

Route to main HT:

HT from osc coil>>Pin 4 of SK4>>Pin 4 of PL4 (from here on also includes HT feed to anode of meter amplifier)>>Pin 7 of SK1>>Pin 7 of PL1>>Connection F on tape deck>>R2>>Switch 1C when set to Record>>Connection 4 on tape deck>>Pin 6 of SK3>>Pin 6 of PL3>>Main HT at the junction of C33/L5.

If that's any help.

Lawrence.

Last edited by ms660; 26th Oct 2020 at 9:57 pm. Reason: missing word...of
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Old 26th Oct 2020, 9:55 pm   #30
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Default Re: Ferrograph Quiet Crackly Audio

Thanks. i didnt see that it splits off at P4 on SK4. I'll do some more probing tomorrow and see what I can find out.
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Old 29th Oct 2020, 3:44 am   #31
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Default Re: Ferrograph Quiet Crackly Audio

Well good news. I got it recording okay. Found out there was a loose wire on the chassis which was part of the oscillator circuit. Only thing is the erase is rather weak. It will erase a recording but only after a few passes. Is there some kind of adjustment for this and would there be any testing points at which I could measure the correct voltage?
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Old 29th Oct 2020, 12:47 pm   #32
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Default Re: Ferrograph Quiet Crackly Audio

Quote:
Originally Posted by MeanDumpsterCat View Post
... the erase is rather weak. It will erase a recording but only after a few passes. Is there some kind of adjustment for this and would there be any testing points at which I could measure the correct voltage?
The erase current could be low but also these machines were designed to erase the tapes of the day. It will struggle to erase many later higher energy tapes.
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Old 29th Oct 2020, 12:56 pm   #33
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Default Re: Ferrograph Quiet Crackly Audio

Check that the erase and bias links are making good contact. Also check that R42 and R43 in the oscillator circuit are good.
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Old 29th Oct 2020, 1:02 pm   #34
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Default Re: Ferrograph Quiet Crackly Audio

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Originally Posted by MeanDumpsterCat View Post
would there be any testing points at which I could measure the correct voltage?
Section 19.1 in the manual.

Lawrence.
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Old 29th Oct 2020, 1:17 pm   #35
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Default Re: Ferrograph Quiet Crackly Audio

Also make sure the erase head face is very clean and that the tape is making intimate contact with the erase head.

David
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Old 29th Oct 2020, 2:27 pm   #36
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Default Re: Ferrograph Quiet Crackly Audio

Thanks. I'll give all those a look. I notice that the testing point for the erase head is tags 2 and gnd but is there any risk of magnetising the head with the multimeter since those tags are connected directly to the erase head winding?
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Old 29th Oct 2020, 2:32 pm   #37
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Default Re: Ferrograph Quiet Crackly Audio

If the erase head should become magnetised it will be demagnetised by the erase current.
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Old 29th Oct 2020, 3:40 pm   #38
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Default Re: Ferrograph Quiet Crackly Audio

Note the erase signal is relatively high frequency at 68kHz, that is why the manual states a valve voltmeter to measure it. If measured with a bog standard multimeter then it will not be measured correctly unless it has a high impedance FET input. Scope is OK but have to convert peak to peak voltage back to rms.

David
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Old 30th Oct 2020, 12:01 am   #39
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Default Re: Ferrograph Quiet Crackly Audio

I dont have a scope. All I have is a digital and analog multimeter. Is there no other way of measuring it?
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Old 30th Oct 2020, 9:35 pm   #40
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Default Re: Ferrograph Quiet Crackly Audio

Unless your digital or analogue meters are spec'd for AC voltage measurement at that sort of frequency (some better ones are) then I personally do not know of an easy/practical way to measure the bias/erase voltages if a scope is not available.

If you had a frequency counter you could measure the frequency (just to prove frequency is in correct ballpark), but it does not help with checking/setting the voltage level.

Can connect a low resistance resistor into the earth return side of the heads and measure the head current by measuring the voltage across the resistor but you would still need a meter capable of measuring high frequency.

Some experienced people (not me) may be able to optimise the recording bias setting by listening tests of the playback of the recorded signal.

David
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