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-   -   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.


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