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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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16th Feb 2020, 1:22 pm | #1 |
Heptode
Join Date: May 2015
Location: Reading, Berkshire, UK.
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Unknown amp with EZ80 EL84 and ECC83 Valves
I have been working on an unknown make of record player that I picked up 2 years ago.
All mechanics etc completed. The amp wasn't working so I replaced several out of spec resistors and changed all the caps apart from smoothing can which I think is OK. The amp is working now but the sound is very low and distorted, I know it's not the cartridge as it works well on another player I have, it's a BSR X5m. I checked the HT which measured 300V which would appear to be correct. My question is if the HT measures OK does it mean that the EZ80 valve is working OK or should I buy a new one and see if it cures the problem? There is a pic of this amp in a thread I started 2 years ago called "record player identification" Les |
16th Feb 2020, 1:29 pm | #2 |
Dekatron
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Location: Wigan, Greater Manchester, UK.
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Re: Unknown amp with EZ80 EL84 and ECC83 Valves
Don’t buy a new EZ80 it appears ok.
What testing have you carried out on the amp, valves voltages, injecting test signals etc to isolate the faulty stage?
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Frank |
16th Feb 2020, 1:46 pm | #3 |
Dekatron
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Re: Unknown amp with EZ80 EL84 and ECC83 Valves
I think this is a well specified amplifier from a 1957 RUCO portable record player. If both stages of the ECC83 are in use. then this will have a really good gain and the BSR X5M will be an ideal cartridge to test it on. Now, regarding your query as to the EZ80, is this connected as a full, or half, wave device?
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Edward. |
16th Feb 2020, 1:53 pm | #4 |
Heptode
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Re: Unknown amp with EZ80 EL84 and ECC83 Valves
Thanks for your replies as yet I have not tested any voltages or done any other tests.
And Edward I believe it's used as a full wave rectifier. |
16th Feb 2020, 1:56 pm | #5 |
Dekatron
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Location: Heckmondwike, West Yorkshire, UK.
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Re: Unknown amp with EZ80 EL84 and ECC83 Valves
The earlier thread: https://www.vintage-radio.net/forum/...d.php?t=146094. No conclusion was drawn then as to the manufacturer.
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16th Feb 2020, 6:05 pm | #6 |
Dekatron
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Re: Unknown amp with EZ80 EL84 and ECC83 Valves
Now I see the photos, I can confirm that this is not a RUCO (Rucogram) product.
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Edward. |
17th Feb 2020, 7:57 am | #7 |
Dekatron
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Re: Unknown amp with EZ80 EL84 and ECC83 Valves
Take some voltage readings, first test the ECC83/EL84 - black test lead to ground/chassis. If the valves are conducting you should have around 200v on the ECC83 anodes, pins 1 & 6 and 300v ish on the EL84. You should have 0v ish on all grids pins 2 & 7 ECC83 pin 2 EL84. Also you should have 250 -300v on g3 pin 9 EL84 Now put black test probe on each control grid, first pin 2, red on pin 3 which is the cathode ECC83, you should have around 1-2v, usually 1.5v, repeat pins 7&8 on the ECC83. Next do the same for the EL84, g1 pin 2, cathode pin 3.
All this will prove the valves are conducting and are within normal operating parameters. If you don't have a scope inject a signal on the EL84's grid through a cap if need be, though it shouldn't be needed, clip the signal onto a screwdriver and touch it on the grid, if ok you'll get an OP, then work your way back touching on each ECC83 grid. If you don't have a scope sig/gen, download Soundcard Scope for your PC/laptop which is free (and brilliant). It includes a decent sig gen, scope and spectrum analyser as well as other stuff. You can use this with your amp at low volume, IE around 1v RMS, use a resistive divider if OP is higher. Andy.
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18th Feb 2020, 9:11 pm | #8 |
Heptode
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Re: Unknown amp with EZ80 EL84 and ECC83 Valves
Hi Andy thank you for taking the time to explain what to check regards to the valves, are the voltages to be taken using DC Range?
I don't have a scope only have a dmm my electrical knowledge is limited but I can check things and solder. I will check what I can and come back with some results. Thanks Les. |
19th Feb 2020, 7:09 am | #9 |
Dekatron
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Re: Unknown amp with EZ80 EL84 and ECC83 Valves
Yes, DC range. I usually write something like this on a notepad HT 1 HT 2, being in order HT at first cap, HT after series resistor, then V1
a g k a g k g/k 1 g/k2 A usefull test whilst taking HT DC readings is to flick the meter onto AC, if over a volt or even in the hundreds on mV, EG 0.785v, the filter cap wants testing. If you don't have a scope, check out SCS I mentioned, you'll just need to make a test lead up IE 3.5mm jack/ lead to two croc clips on red and shield. A scope and sig gen makes testing amps a lot easier. Andy.
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19th Feb 2020, 12:14 pm | #10 |
Dekatron
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Re: Unknown amp with EZ80 EL84 and ECC83 Valves
It would help to know whether your DMM is a 1M or 10M resistance input if looking at any high impedance voltages such as low current anode voltages or grid voltages. The instruction leaflet may help here or at least info on the make and model.
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