Argyll Minor reel to reel help needed.

[ms660]

Ah...Didn't know that the heater winding was centre tapped, cheers for that.

Lawrence.

[sobell1980]

Thankyou for confirming that for me. Looks like the valves are ruined then? Even though the heaters are showing continuity I expect the short caused other damage inside the valves. This means I guess I will also need to replace v2 which is the recording level indicator. I think the short from v1 anode to the heater pins 4 and 5 of valve 1 has ruined all the valves. I was hoping to see the heaters open circuit to prove my point.
Dave.

[ms660]

If the heaters are showing continuity then they should glow if sufficient heater voltage is applied to them.

As said earlier, I don't have the schematic but you said in an earlier post that you might have shorted the anode of one half of the ECC83 to the heater pins, the anode of that is probably fed via a high (ish) resistor, if that's the case then I wouldn't have thought that would have damaged the valves.

Lawrence.

[Cobaltblue]

I agree with Lawrence.

Very unlikely you have damaged the filaments that way.

I know this may be completely wrong but you do have the valves in the correct sockets

If they were wrong due to the different filament arrangements neither would light ( well the ecc83 might just get a slight glow).

Cheers

Mike T

[AndiiT]

Hi, just a thought reading through your previous posts, is it likely that your (accidental) short circuit has damaged the tracks on the pcb which feed the valve heaters?, it might be worth removing the valves and the connections from the transformer heater winding to the pcb and checking the continuity of the tracks.

Another possibility is that you have connected one of your replacement capacitors incorrectly (I know, I've re-capped a few Fidelity machines and it's an easy mistake) or dislodged another connection somewhere.

Regards

Andrew

[sobell1980]

Ok I've gone back and checked valves in correct places. Checked heaters are receiving voltage, approx 3.7 v ac each. High tension is way too high. V1 anodes receiving 320 volts DC and v3 anode receiving 350 V DC. Checked MR1 and I have 270 volts ac going in and approx 320 v DC coming out. Still no sign of the heaters getting hot. HT is way too high.
Dave.

[sobell1980]

I've just put a silicon diode in MR1 place. I have 270 volts ac going in and 360 volts DC coming out my replacement diode. I guess I need to fit a dropper to get the HT correct. You would expect the valves to be doing their nut but nothing.

I also expect if I replace the large electrolytics (smoother) etc it will help bring down the HT also and measure the HT again before I fit a dropper after the diode.

[ms660]

Trace the heater voltage from the transformers heater winding through to the valves and at various points along the way. According what Julie said earlier the heater winding is centre tapped so it's the two outer connections (on the schematic) you need to measure from and trace through to the valves.

EDIT: If the heaters aren't glowing normally then the HT will be high.

Lawrence.

[sobell1980]

I'm getting myself confused now. I've been looking at the service data sheets for ECC83 valve's. It quotes the heater voltage should be 6.3 volts for its heaters. I measure with my probes from pins 4 and 5 to pin 9
I get 3.7 volts. So half the quoted voltage from the data sheet. Why am I not measuring 6.3 volts? This us what the valve needs to make the heater work. If I measure across the pair of wires out of the transformer I get 7.5 volts. If I measure from each wire to chassis ground I get 3.75 v, the same as when I measure at the heater pins. So is my LT voltage right or wrong? I'm seeing that the heaters should be getting the 7.5 v but are only receiving half that.I'm confusing myself I think. Many thanks.
Dave.

[ms660]

See post#28.

Lawrence.

[Station X]

If you're seeing 7.5V at the transformer then you should also see 7.5V at the point where the wires from the transformer connect to the circuit board.

That being the case check the voltage at various points between the PCB lands which the wires connect to. This is simple DC continuity testing.

If you're convinced it's the valves remove them. The correct heater voltages should still be present.

[Station X]

Looking at the circuit, the heater winding centre tap doesn't go to chassis.

R12 an 8.2R resistor is connected in series with the EL84's heater. Is it intact? Check it with the EL84 removed.

[Station X]

8.2R just happens to be the hot resistance of an EL84's heater, so I'd expect to see at least 6.3V or more between pins 4 and 5 of the EL84 and a similar voltage across R12.

[Station X]

Having read previous posts I see that this recorder uses the Fidelity Playmaster circuit rather then the Fidelity Argyll Minor circuit. Apologies for confusing the issue.

The heater centre tap isn't grounded in the Playmaster either, so heater voltages will need to be measured wrt the centre tap.

[ms660]

I'm confused now, the OP's photo's show it to be an Argyll Minor, anyways whichever, I've found an online schematic for what is supposed to be the Argyll Minor, in that schematic the centre tap of the heater winding is connected to the cathode of the EL84.

The centre tap and one half of the winding also feeds the DM70 heaters via an 82 ohm resistor.

For the above mentioned schematic another test for the heater voltage would be to measure the voltage between the cathode of the EL84 and pin 4 and then pin 5 to see what's what then ditto for the ECC83 (pins 4/5 and then pin 9)

Lawrence.

[Station X]

Confusion reigns then. I was just going by what it says in posts 16 and 17.

A circuit diagram shouldn't be necessary to sort heater wiring in any case.

[ms660]

I note that etched on the pcb is A M 1.

This might not be anything as it doesn't tally up with what the OP has reported but look at the pcb track that runs between pin 4 of the EL84 and pin 9 of the ECC83, there's a connection land roughly half way along where one of the heater feeds from the transformer is connected, does that look like a crack at the bottom of it or is it something else like a streak of flux or something?

I agree, if the heaters aren't lighting it should be an easy fix.

The plot thickens.

Lawrence.

[Welsh Anorak]

Hi
This is a fault best sorted cold - i.e. check for open and/or shorts between heater pins, not forgetting the 'magic eye'. It's possible a partial short due to a solder splash is loading the AC feed. Many of these machines went through lots of design changes so any circuit will be an approximation to the one you've got.
Glyn

[Top Cap]

The quoted 1 Ohm measurement of the EL84 Heater seems low. I suspect that the heater line is being connected to the EL84 Cathode to elevate it in potential to reduce hum. However a cathode to heater short in the EL84 would probably knock out one side of the heater supply. Just a thought - what is the heater voltage on the ECC83 with the EL84 pulled?

[sobell1980]

I managed the other day to get it all working . It burst into life after probing the circuit board valve pins and all of a sudden it burst into life. I loaded the tape and was playing music well apart from a noisy volume pot. I have sprayed the pots with servisol to clean them and free them up.
I thought I would try the tape again. Same scenario as before. No voltage to heaters of valves. I checked across pins 3 and 4 to pin 9 of the ECC83 and pins 4 to 5 of the EL 84. No voltage whatsoever. When the set was working I checked my LT and HT, all in spec at all the right places.
I've tested where the heater wires terminate at the pcb and nothing. I've removed the heater wires from the pcb and tested with my meter across the two disconnected heater wires, I get approx 20 volts. Reconnecting them back to the pcb they read 0.00 volts as soon as they are connected back to the pcb. Most strange, any ideas?
Many thanks.
Dave