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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 23rd Jul 2022, 8:59 pm   #41
Uncle Bulgaria
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Default Re: Starting out with a Ferrograph series 4

This sounds like the same metal fatigue problem I experienced. You need to think logically about what you're measuring and why, and refer back to the circuit diagram. Mark the wire colours and trace them back so you know what you're measuring. Draw diagrams in a book as you go.

One of the tags you've marked is grounded to the chassis, so it's very unlikely there's 10VAC there. The fact they're all '10VAC' implies a measurement error.

There are two tag strips on my 4A top plate. One for the 'Plug Attached To Deck' and one for the 'Socket Attached To Deck' shown in the circuit diagram, marked 1-8 and Y, A, Gr, B, C, D, E, F. Follow the wire colours back to the plug and socket assemblies, and mark up the circuit diagram to remind you where goes where with what colour.

The voltage readings you took in post #31 are not far off for Vs 1 & 2. Recall the note below the table: "Voltage readings are approximate..." It is awkward to work out the right pins upside-down. V3 is low. You haven't posted the results of the first page of alignment values in post #30 ("Voltage between chassis and input to smoothing choke L4" etc. on both playback and record). That lets you know the PSU is working properly.
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Old 23rd Jul 2022, 11:07 pm   #42
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Default Re: Starting out with a Ferrograph series 4

Certainly it is tricky. In my copy of the manual the tag numbering jumps from 5 to 7 and the last tag is illegible... kind of 8 with a handwritten 6 next to it. I am tracking the wires to make sense of it all. I think the connections are OK. In the sense the machine runs and plays tape.. the audio isn't too good but it plays.
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Old 23rd Jul 2022, 11:44 pm   #43
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Default Re: Starting out with a Ferrograph series 4

Had another close look at the tags.

Tag
3 reading 1.6 VAC
7 240 VAC
8 (6) 20 VAC
4 (PLAY) 2.3 V DC

4 (REC) 276V DC


I am thinking that some caps in the bias supply must be off. I wasn't expecting 276 V on this line.
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Old 24th Jul 2022, 11:03 am   #44
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Default Re: Starting out with a Ferrograph series 4

Quote:
Originally Posted by phil_fw View Post

4 (REC) 276V DC


I am thinking that some caps in the bias supply must be off. I wasn't expecting 276 V on this line.
4 in the schematic is the HT feed to the oscillator, given as 240 VDC in the manual when set to record.

Lawrence.
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Old 24th Jul 2022, 2:22 pm   #45
phil_fw
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Default Re: Starting out with a Ferrograph series 4

I see so it comes from the switch on the deck to energise the bias oscillator?
I have another problem now... the thyristor TH1 is open circuit. No value or even range of values is listed for this component.
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Old 24th Jul 2022, 2:58 pm   #46
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Default Re: Starting out with a Ferrograph series 4

Quote:
Originally Posted by phil_fw View Post
I see so it comes from the switch on the deck to energise the bias oscillator?
I have another problem now... the thyristor TH1 is open circuit. No value or even range of values is listed for this component.
1) Yes, that's correct, switch 1C.

2) It's not a thyristor it's a thermistor, the components list lists it as a STC A1 522/100.

In another thread Uncle B measured the value of it at room temperature as 110kOhm, I would think that would be with the thermistor out of circuit (Post#49):

https://www.vintage-radio.net/forum/...=151194&page=3

Lawrence.

Last edited by ms660; 24th Jul 2022 at 3:16 pm. Reason: deletion
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Old 24th Jul 2022, 4:34 pm   #47
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Default Re: Starting out with a Ferrograph series 4

oops I mispoke thanks.
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Old 24th Jul 2022, 4:48 pm   #48
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Default Re: Starting out with a Ferrograph series 4

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Originally Posted by phil_fw View Post
oops I mispoke thanks.
No problem.

So far as I can make out the thermistors resistance at 20 degrees C should be between 80kOhm to 120kOhm, it's there to hold the oscillators control grid drive constant at a level that prevents unwanted harmonic generation.

Lawrence.
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Old 26th Jul 2022, 6:07 pm   #49
phil_fw
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Default Re: Starting out with a Ferrograph series 4

My Series 4 is playing OK. Sounds pretty good. Still a total absence of any record function though. I cannot find a trace of bias signal (between deck tags 1&2 and 1&3 ?) and nothing is erased when I try to record. Swapped out the thermistor, which was open circuit, and checked the power on valve V6 - which is a new EL84. The HT power comes on when deck is switched to record and I get about 266V on both anode and grid. A little baffled.
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Old 26th Jul 2022, 6:37 pm   #50
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Default Re: Starting out with a Ferrograph series 4

Quote:
Originally Posted by phil_fw View Post
My Series 4 is playing OK. Sounds pretty good. Still a total absence of any record function though. I cannot find a trace of bias signal (between deck tags 1&2 and 1&3 ?) and nothing is erased when I try to record. Swapped out the thermistor, which was open circuit, and checked the power on valve V6 - which is a new EL84. The HT power comes on when deck is switched to record and I get about 266V on both anode and grid. A little baffled.
When posting valve grid voltages you should specify which grid, for pentodes it's usually g1, g2, g3.

Those terms are the ones most commonly used by the valve manufactures:

http://www.r-type.org/pdfs/el84.pdf

Measuring the valves cathode voltage can also sometimes give a clue as to what is or isn't happening.

Lawrence.
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Old 26th Jul 2022, 9:17 pm   #51
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Default Re: Starting out with a Ferrograph series 4

Just a double check, have you checked your erase link and dummy octal plug (with wire link) are fitted as per my Post # 22 ?

I assume your grid voltage must be g2 (screen grid) pin 9 of the EL 84, somewhat strange if your anode and g2 voltages are exactly the same, would expect g2 to be lower.

David
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Old 28th Jul 2022, 1:04 am   #52
phil_fw
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Default Re: Starting out with a Ferrograph series 4

I read your comment again and poured over the manual. The erase link yes.. the octal plug thing didn't make any sense to me. I could not imagine what that functionality would be for. Finally the words got through.. and I fished around for the plug. I did have one but I got confused and thought it had come off the series 5 lurking on the floor. I checked that pins 3 and 4 were linked and plugged it in. And lo... the oscillator valve did light up. Now the machine records and plays.

Thanks for all the tips.

[Phil
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Old 28th Jul 2022, 8:54 am   #53
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Default Re: Starting out with a Ferrograph series 4

Very good news.

While it is working correctly I would take a fresh set of valve voltage readings both in Playback and Record modes, also measure the erase and bias signals in Record mode, for future reference.

David
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