UK Vintage Radio Repair and Restoration Discussion Forum

UK Vintage Radio Repair and Restoration Discussion Forum (https://www.vintage-radio.net/forum/index.php)
-   Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players (https://www.vintage-radio.net/forum/forumdisplay.php?f=35)
-   -   Ferrograph Quiet Crackly Audio (https://www.vintage-radio.net/forum/showthread.php?t=172217)

MeanDumpsterCat 18th Oct 2020 7:57 pm

Ferrograph Quiet Crackly Audio
 
Hello. I've recently been working on a Ferrograph Series 5.

I've sorted out most of the major problems it had however when I was replacing some of the resistors and capacitors in the amplifier (since they had gone quiet out of spec) a new problem has come up.

The audio had gone extremely quiet and there's a noticeable crackling noise even with the gain at 0. Also no hum that I can usually hear with valve equipment.

The meter also no longer moves down to zero when in record mode and it does not erase the tape (it did before).

I tried giving the valves a wiggle when it was on to see if it was a loose socket connection but no such luck.

Any pointers on places I should start looking?

Cheers.

barrymagrec 18th Oct 2020 8:04 pm

Re: Ferrograph Quiet Crackly Audio
 
Power supply. Check the HT voltage. EZ80 would be the favourite suspect.

DMcMahon 18th Oct 2020 10:17 pm

Re: Ferrograph Quiet Crackly Audio
 
If nothing obvious found bad then double check your previous work of component replacements, quite easy when changing multiple components to fit incorrect value component / connect to incorrect place / inadvertently disturb another component/connection, I have done it myself.

David

TIMTAPE 18th Oct 2020 10:28 pm

Re: Ferrograph Quiet Crackly Audio
 
Also check polarised components such as
capacitors for correct installation.

MeanDumpsterCat 19th Oct 2020 12:18 pm

Re: Ferrograph Quiet Crackly Audio
 
Thanks. I did also desolder the filter cap to test for leakage so I may have disturbed some wiring in the power supply and not to mention those stiff octal connectors that require quite a bit of wiggling to remove. I'll take a proper look at it this evening.

MeanDumpsterCat 19th Oct 2020 6:28 pm

Re: Ferrograph Quiet Crackly Audio
 
3 Attachment(s)
Okay so I had a look at the power supply.

I noticed that one of the wires of the ECC82 is damaged though it seemed to check out okay with the multimeter.

I also cleaned the valve sockets with de-oxit without much luck.

Its also worth noting that the amp did take a bit of a knock on the workbench by accident however I couldnt see anything that's damaged.

Would it be possible that the damaged connection would be okay on the 4V from my multimeter but cause issues when at higher voltages.

According to the pinout, the break is on the second grid of the ECC82

I am still thinking the fault resides in the amplifier though. I'm just not sure if a poor connection on the ECC82 oscillator would cause lack of volume an no erase. Please correct me if i'm wrong.

MeanDumpsterCat 19th Oct 2020 6:43 pm

Re: Ferrograph Quiet Crackly Audio
 
1 Attachment(s)
Picture of the amplifier incase a more expert eye can spot something wrong.

I have since tidied up the soldering a little but again, made no difference.

DMcMahon 20th Oct 2020 1:06 pm

Re: Ferrograph Quiet Crackly Audio
 
Quote:

Originally Posted by MeanDumpsterCat (Post 1301331)
I noticed that one of the wires of the ECC82 is damaged though it seemed to check out okay with the multimeter.

Would it be possible that the damaged connection would be okay on the 4V from my multimeter but cause issues when at higher voltages.

According to the pinout, the break is on the second grid of the ECC82

I am still thinking the fault resides in the amplifier though. I'm just not sure if a poor connection on the ECC82 oscillator would cause lack of volume an no erase. Please correct me if i'm wrong.

Looks like heat damage to the cable insulation from soldering iron, so should be OK. If the ECC 82 is just for the oscillator, then even if it had a fault would not expect it to affect playback volume.

Have you checked the EZ 80 HT voltage yet ? If OK then check the valve electrode voltages and see how they compare to schematic values, mainly anode, cathode and G2. Also should not expect to see much if any +ve DC voltage at the Control grids G1, unless previous valve anode to grid coupling capacitor is passing DC/leaking.

David

DMcMahon 20th Oct 2020 1:30 pm

Re: Ferrograph Quiet Crackly Audio
 
On the Series 5 schematic I am now looking at (in Service Manual) I see that the valve electrode voltages are not shown on the schematic, but they are listed in the manual.

Note - that the second grid of the ECC 82 you referred to, identified on the schematic as g" is the second Control grid (G1) of that valve, i.e. not the G2 I referred to, which is the Screen grid (not present on ECC 82).

David

MeanDumpsterCat 20th Oct 2020 1:39 pm

Re: Ferrograph Quiet Crackly Audio
 
Quote:

Originally Posted by DMcMahon (Post 1301592)
Looks like heat damage to the cable insulation from soldering iron, so should be OK. If the ECC 82 is just for the oscillator, then even if it had a fault would not expect it to affect playback volume.

Have you checked the EZ 80 HT voltage yet ? If OK then check the valve electrode voltages and see how they compare to schematic values, mainly anode, cathode and G2. Also should not expect to see much if any +ve DC voltage at the Control grids G1, unless previous valve anode to grid coupling capacitor is passing DC/leaking.

I havent had a chance to check all the voltages yet but i'll certainly give that a go. I did have a spare EZ80 valve so I swapped them over to see if there was any difference and didnt have much luck.

Welsh Anorak 21st Oct 2020 9:51 am

Re: Ferrograph Quiet Crackly Audio
 
As the crackling is evident with the volume at zero, I'd be inclined to suspect an output stage fault. As David says, check the HT is constant at around 300v. Then maybe check the output valve by substitution. I assume you've replaced the coupling capacitor?

barrymagrec 21st Oct 2020 10:06 am

Re: Ferrograph Quiet Crackly Audio
 
Since the erase level is down and the meter fails to zero I think if not a power supply fault then something pulling it down, could be excess current through the EL84 or a leaky / reversed electrolytic.

MeanDumpsterCat 21st Oct 2020 10:54 pm

Re: Ferrograph Quiet Crackly Audio
 
1 Attachment(s)
Quote:

Originally Posted by Welsh Anorak (Post 1301850)
As the crackling is evident with the volume at zero, I'd be inclined to suspect an output stage fault. As David says, check the HT is constant at around 300v. Then maybe check the output valve by substitution. I assume you've replaced the coupling capacitor?

Thanks. I'll double check that I havent unintentionally wired any of the capacitors the wrong way. Its unlikely but I did de-solder some of the capacitors in the power supply when checking them for leakage.

I did replace some electrolytic in the amplifier but those are fine.

I do seem to recall that there was a bit of leakage on either C34 or 33 though it wasnt very much, but it might be just enough to be causing an issue now.
I put off replacing them since they in one of those multi-section cans and would require fiddly work to replace them properly.

I'm led to believe this since the problem was intermittent before but is now permanent.

Included a snap of the schematic showing the caps I seem to recall being leaky.

I'll definitely double check them when I get time (may be a few days since i'm very busy with work at the moment. Hence slow progress).

martin.m 21st Oct 2020 11:56 pm

Re: Ferrograph Quiet Crackly Audio
 
I would start by feeding the line out signal from a CD player into the grid of the output stage (pin 2 if it's an EL84) and see if clear sound is produced.

MeanDumpsterCat 22nd Oct 2020 1:19 am

Re: Ferrograph Quiet Crackly Audio
 
Hm. Does anyone know what the voltages of the EZ80 should be? Doesnt seem to list it in the manual annoyingly.

DMcMahon 22nd Oct 2020 8:50 am

Re: Ferrograph Quiet Crackly Audio
 
Do not know the actual values when in a Series 5. A shame the manual does not list them.

Heater voltage would expect to be 6.3VAC, this is off a separate transformer winding to the heater supplies for the other valves which is listed as 6.3V

The AC voltage across the anodes will be at least 500 volts and could be as high as 750 volts, depending upon the actual transformer secondary winding output. This winding has a centre tap, so it would be safer to measure each anode to the centre tap, i.e. lower/approx half voltage.

The cathode is the rectified DC output, in the manual it is referenced as 285 volts in Playback mode. i.e. "input to smoothing choke L5".

All voltages are approximate, the rectified DC output can vary somewhat depending upon load and reservoir/smoothing capacitor condition.

Be extremely careful measuring the high voltages.

David

MeanDumpsterCat 25th Oct 2020 2:49 pm

Re: Ferrograph Quiet Crackly Audio
 
So good news. I've got it playing okay. I found a capacitor that wasnt properly connected despite my multiple re-checks.

However, while it does record it is not erasing the previous recording, the meter does not reset to zero and the meter bulb seems to turn off randomly.

Guess I still have some more searching to do.

ms660 25th Oct 2020 4:52 pm

Re: Ferrograph Quiet Crackly Audio
 
If the erase head is clean and it's head to tape contact is ok check the HT feed to the meter amplifier and the erase oscillator when set to record as they share a common feed via R2 etc.

Lawrence.

MeanDumpsterCat 25th Oct 2020 6:06 pm

Re: Ferrograph Quiet Crackly Audio
 
Thanks i'll definitely give that a look.

I noticed there are some capacitors coupling the grids of the oscillator and they appear to be the silver "Suflex" capacitors which I heard rarely fail but tend to intermittently go completely open circuit when they do.

This was an intermittent fault before but now its permanent. Wondering if they could have anything to do with it.

I'll check the HT voltages first but I have my suspicions about those caps based on what i've read on some old threads here.

barrymagrec 25th Oct 2020 6:10 pm

Re: Ferrograph Quiet Crackly Audio
 
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.

ms660 25th Oct 2020 6:19 pm

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.

MeanDumpsterCat 25th Oct 2020 11:33 pm

Re: Ferrograph Quiet Crackly Audio
 
Quote:

Originally Posted by barrymagrec (Post 1303585)
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.

MeanDumpsterCat 26th Oct 2020 7:44 pm

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

barrymagrec 26th Oct 2020 7:52 pm

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.

ms660 26th Oct 2020 7:55 pm

Re: Ferrograph Quiet Crackly Audio
 
What about the anode of V5 (ECC83) the anode that's connected to pin 7 of SK1?

Lawrence.

MeanDumpsterCat 26th Oct 2020 8:03 pm

Re: Ferrograph Quiet Crackly Audio
 
Quote:

Originally Posted by barrymagrec (Post 1303930)
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:

Originally Posted by ms660 (Post 1303932)
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.

barrymagrec 26th Oct 2020 8:11 pm

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.

MeanDumpsterCat 26th Oct 2020 8:20 pm

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.

ms660 26th Oct 2020 8:30 pm

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.

MeanDumpsterCat 26th Oct 2020 8:55 pm

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.

MeanDumpsterCat 29th Oct 2020 2:44 am

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?

TIMTAPE 29th Oct 2020 11:47 am

Re: Ferrograph Quiet Crackly Audio
 
Quote:

Originally Posted by MeanDumpsterCat (Post 1304767)
... 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.

barrymagrec 29th Oct 2020 11:56 am

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.

ms660 29th Oct 2020 12:02 pm

Re: Ferrograph Quiet Crackly Audio
 
Quote:

Originally Posted by MeanDumpsterCat (Post 1304767)
would there be any testing points at which I could measure the correct voltage?

Section 19.1 in the manual.

Lawrence.

DMcMahon 29th Oct 2020 12:17 pm

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

MeanDumpsterCat 29th Oct 2020 1:27 pm

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?

barrymagrec 29th Oct 2020 1:32 pm

Re: Ferrograph Quiet Crackly Audio
 
If the erase head should become magnetised it will be demagnetised by the erase current.

DMcMahon 29th Oct 2020 2:40 pm

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

MeanDumpsterCat 29th Oct 2020 11:01 pm

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?

DMcMahon 30th Oct 2020 8:35 pm

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

MeanDumpsterCat 3rd Nov 2020 2:42 am

Re: Ferrograph Quiet Crackly Audio
 
Hi. Just thought id update this thread.
I managed to fix the faults.

There was a disconnected wire on the tape deck chassis which was causing the lack of HT and the no erase fault was much simpler. The erase plug on the back had fallen out without me noticing. Sticking that back in everything started working.

Sounding a lot better with the new capacitors anyhow. Still havent properly looked at the canned caps but to be honest they measured okay and the machine is working perfectly so i'm going to leave them for now.

I'll be honest the sound quality really surprised me. Both through the internal speaker and playing it's recordings on my hifi r2r. Definitely going to have a lot of fun with this machine now its all working. Great for making tape loops with the built in splicing block.

Thanks for all the help anyway :)

DMcMahon 3rd Nov 2020 9:06 am

Re: Ferrograph Quiet Crackly Audio
 
Great feedback.

barrymagrec 3rd Nov 2020 9:11 am

Re: Ferrograph Quiet Crackly Audio
 
Good work.


All times are GMT. The time now is 6:07 am.

Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.