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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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18th Jul 2022, 11:53 am | #21 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
Thanks Uncle, I will take care. Neither my series 4 nor series 5 seem to be oscillating. I will start there. The HT supply is OK now.
I will probe the amplifier stages too and see if the DC blocking capacitor is shot. |
18th Jul 2022, 3:51 pm | #22 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Starting out with a Ferrograph series 4
Check on both that the heaters of the bias oscillator valve is lit up (powered), V6 on Series 4 and V4 on series 5 (both EL 84) when Record selected.
For the Series 4, a dummy octal plug (with pins 3 and 4 linked) needs to be fitted into the "AUX. SOCKET 2" (SK 10 on schematic) to complete the heater circuit for V6 or wire link directly at SK 10 pins. Also the "ERASE LINK" should be fitted. These are on the rear panel of the Supply Panel. For Series 5 the "BIAS & ERASE" link should be fitted on the rear of the Supply Panel. David Last edited by DMcMahon; 18th Jul 2022 at 4:09 pm. Reason: Update |
18th Jul 2022, 5:14 pm | #23 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
Yes! Silly me.. I was assuming it would be active when power was on and just switched in when bias required.
I did re-assemble the series 5 machine with new EZ80 and it played a tape! Though.. it was a little quiet and distorted. Heads are clean and I think the amplifier circuit is out of kilter. When I increased the gain gently it started with a "whump whump whump" sound. I turned it off. |
18th Jul 2022, 6:01 pm | #24 |
Nonode
Join Date: May 2016
Location: Cornwall, UK.
Posts: 2,315
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Re: Starting out with a Ferrograph series 4
Whump whump whump sounds like 'motorboating'. Filter/reservoir capacitor the likely culprit, as on the Series 4. Replacing that cured the same issue for me, though perhaps yours will recover with some reforming through being 'on' for a while.
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19th Jul 2022, 9:59 am | #25 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
Just a quick question. I was operating my machine with the top plate raised and noticed some fairly impressive sparks from the speed switch when changing speeds. Is this normal? This machine (it was the series 5 which seemed nearer to operation than the 4 I was tinkering with) played a tape OK.. dodgy audio though and the aforementioned motorboating - but changing speed produced this sparks and what sounded like a fairly sharp crack from within.
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19th Jul 2022, 12:08 pm | #26 | |
Pentode
Join Date: Nov 2010
Location: Tenby, Pembrokeshire, Wales, UK.
Posts: 139
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Re: Starting out with a Ferrograph series 4
Quote:
Bill |
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19th Jul 2022, 1:46 pm | #27 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
Thanks Bill I'll check it out.
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20th Jul 2022, 7:48 pm | #28 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
More on motorboating - still trying to decrypt the schematic and follow the signal chain. Today... gave the machine a quick spin.. the motorboating started when the gain was increased a little.. then went away as the gain was increased further. I don't think the complete amplifier circuit is operating yet and I still working through each valve in the chain and trying to measure the voltages on the pins. I do have a series 4 manual but the print is a little grainy.
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20th Jul 2022, 9:09 pm | #29 |
Pentode
Join Date: Dec 2009
Location: Chatteris, Cambridgeshire, UK.
Posts: 176
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Re: Starting out with a Ferrograph series 4
Amplifier instability can occur if the unit is set to record and the gain increased with no input connected.
However, motorboating when set to playback is not normal of course. A possibility is dirty or tarnished switch contacts on the main deck mode switch. The speed should only be altered when in stop mode, but as Bill mentions above, leaky suppression capacitors can be causing motors to be partly energised when they should not be.
__________________
Andrew Last edited by PYE 405; 20th Jul 2022 at 9:27 pm. |
20th Jul 2022, 9:54 pm | #30 |
Nonode
Join Date: May 2016
Location: Cornwall, UK.
Posts: 2,315
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Re: Starting out with a Ferrograph series 4
As I mentioned before, a proper 'Manual of the Ferrograph' is invaluable. There are lots around, starting on eBay for 1.50 or a Series 4 for £7.50. I got mine from the enormously helpful Terry Martini-Yates (of this parish and Ferrographworld.com).
I've attached the relevant pages from the Series 4 manual which show the voltage readings from which you should be able to see if anything's up. |
21st Jul 2022, 11:12 am | #31 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
I had a probe around the amplifier -
Simple question hmm do I measure the voltages with the valves in or out? Quite the tangle of wires on the tags and not easy to orient the pins from below.. But I made some measurements: Anode Grid Cathode V1 140 73 less than 1V V2 60 82 1.5 V3 60 82 1.9 V4 139 negligible DC volts on any other pin I will check them again. For sure V1 seems a little high compared to the manual. |
21st Jul 2022, 1:19 pm | #32 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
So I injected an audio signal into Input 1 and then Input 2. Both worked well.. with good amplification of the signal. Now I am wondering why playing tape does not produce any sound. Perhaps the whup-whup-whup was a result of having the inputs floating?? No whup-whup with an injected signal. Is it the play head? It's progress ... slow... but coming.
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21st Jul 2022, 1:42 pm | #33 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Starting out with a Ferrograph series 4
Injecting a signal via the jack sockets isolates the first amplifier stage for the playback, the source of the instability might be in that stage, eg: V1's g2 and anode supply de-coupling capacitors C9 & C11.
Lawrence. |
21st Jul 2022, 2:09 pm | #34 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
Thanks Lawrence I have a feeling I am getting closer...
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21st Jul 2022, 2:27 pm | #35 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Starting out with a Ferrograph series 4
It would be worth checking all the HT related electrolytic capacitors at least, C9, C11, C12, C13, C24, C26, C29 and C30 including C30's plug and socket connections (Pin3 of SK5 & pin 3 of P5)
Lawrence. |
21st Jul 2022, 3:15 pm | #36 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
Yes... changed the capacitors and it is behaving itself a lot better. Managed to play a tape.
A little strange when attempting record. The tape has audio. I stop and record some signal over it. Rewind and press play. There is silence but nothing is recorded. Also... the silence just continues beyond the duration of the attempted recording. As if the machine now won't play audio from the tape. I turned it of for a while to let it gather its wits - but no dice. The tape is silent now. |
21st Jul 2022, 8:57 pm | #37 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Starting out with a Ferrograph series 4
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21st Jul 2022, 11:18 pm | #38 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Starting out with a Ferrograph series 4
Strange that after playing a tape reasonably well, it later is just silence ?
In Post 31 you did not list a voltage for V4 (output valve) Screen Grid, was this an omission ? the anode voltage result also was much lower than value in the manual. I think you should closely recheck all the main valve voltages. David |
21st Jul 2022, 11:50 pm | #39 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
You are right.. I am on it!
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23rd Jul 2022, 2:06 pm | #40 |
Triode
Join Date: Jun 2022
Location: Sheffield, South Yorkshire, UK.
Posts: 32
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Re: Starting out with a Ferrograph series 4
Hi all
I think I am having a problem with the tag strip on the deck. Some of the wires came adrift. There used to be a paper strip to number the tags but it clearly came off some time ago. I checked the tags with the voltmeter. Something is amiss. Phil |