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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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26th Jul 2022, 8:56 pm | #41 |
Triode
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Re: AR88D gone low audio output
Hi graham
Thanks for reply Yes it is the correctly marked , metal , valve ….will get a new one to try . So many helpful people on here prepared to try and help newcomers. Will let everyone know if a new valve does the trick Regards Steve G4HTZ
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G4HTZ ASHEN ESSEX Restored a VIKING 2 AM TX Now playing with a AR88….. |
26th Jul 2022, 9:03 pm | #42 | |
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Re: AR88D gone low audio output
Quote:
Is R38 OK? You could try monitoring the valve's anode voltage from the time power is applied to see if it drops instantly or when the valve warms up.
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26th Jul 2022, 9:24 pm | #43 |
Triode
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Re: AR88D gone low audio output
Sorry forgot to say R38 reads 1.65M so slightly high
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26th Jul 2022, 9:26 pm | #44 |
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Re: AR88D gone low audio output
That won't be the problem then.
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27th Jul 2022, 6:24 pm | #45 |
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Re: AR88D gone low audio output
Might be also worth checking/computing V10's g1 bias voltage, less bias voltage means lower anode voltage.
Lawrence. |
27th Jul 2022, 6:42 pm | #46 |
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Re: AR88D gone low audio output
I trust the cap from anode of output valve to chassis has been changed and put across primary? Forgive me if I have missed this
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27th Jul 2022, 9:27 pm | #47 |
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Re: AR88D gone low audio output
Beware of RCA's original AR88 manual, they use the 'M' letter for the x1,000 multiplier and use 'meg' for the x1,000,000 multiplier.
It's caught a lot of people out, so double checking is a good idea. David
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27th Jul 2022, 9:42 pm | #48 | |
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Re: AR88D gone low audio output
Quote:
Also check R36, R27. Bias voltage has to be measured between cathode and grid.
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27th Jul 2022, 10:14 pm | #49 | |
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Re: AR88D gone low audio output
Quote:
Not sure if I have checked this cap …will do so tommorow Thanks Steve
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27th Jul 2022, 10:16 pm | #50 | ||
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Re: AR88D gone low audio output
Quote:
Yes resistors have been changed previously and values are correct Will check the bias voltage as you suggest Thanks Steve
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27th Jul 2022, 10:18 pm | #51 | |
Triode
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Re: AR88D gone low audio output
Quote:
Yes did confuse me initially….but that’s not hard too do … But gradually working my way through the set with the help of everyone on here Regards Steve
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28th Jul 2022, 10:51 am | #52 | |
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Re: AR88D gone low audio output
Quote:
Lawrence. |
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28th Jul 2022, 12:00 pm | #53 |
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Re: AR88D gone low audio output
That's interesting.
I have an early AR88 from before the suffix letters. It has a PVC wiring harness which is very professionally fitted and seems to date back to a refurb in the early fifties. I think it was at REME. There is a label inside, I remember. It's been messed with a fair amount, but I came across the HT link when I was building an HT inverter for it, about 1970. It wasn't a successful project. I needed a 5v car battery for the heaters and a 12v one for the inverter. Efficiency was too low trying from 6v and I wasn't about to rewire all the heaters to do 12v/6v selectable. I've come across a number of discrepancies between it and the AR88D manual diagram both connections and component values. It looks like I've just stumbled across another one. When I next have it apart, I'll have a look around. I think it's a link in the HT path, but it could be HT back inside for something else. The audio output transformer and wiring is the very early arrangement with various output impedances and the PVC loom is for two headphone jacks. At some time there had been a product detector bodged in under the chassis. At a guess from a Shortwave Mag article knowing the reading habits of the former owner and his friends. The worst mod was the tuning scale. The former owner (a pharmacist) had tried cleaning the main tuning scales and succeeded in cleaning some of the scale off. He replaced it by hand in blue ballpoint! At a G-QRP Rochdale doo in the late 80s, I found a brand new tuning scale on a rally stall. Double-bagged AND it was the all yellow early type, not the alternating yellow/black/yellow that came soon after. OK, so mine's rather atypical. I never noticed the difference in links. David
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28th Jul 2022, 12:19 pm | #54 |
Triode
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Re: AR88D gone low audio output
Well new valve arrived a new old stock …plugged it in and you guessed it still the same .
Unfortunately no time to delve any further as we now have a moving date so started boxing the shack up …..amazing how much rubbish you keep from years ago that you think will come in handy one day but never has Thanks for all the help will try and get back on the AR88 in a few months Regards Steve G4HTZ
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28th Jul 2022, 12:57 pm | #55 |
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Re: AR88D gone low audio output
That cap I mentioned by the way, needs to be across the o/put tx primary. If it fails, goodbye tx.
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28th Jul 2022, 1:43 pm | #56 | |
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Re: AR88D gone low audio output
Quote:
Will look at it next time round See it currently goes from anode to earth 3n cap
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28th Jul 2022, 4:25 pm | #57 | |
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Re: AR88D gone low audio output
Quote:
Martin
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28th Jul 2022, 4:58 pm | #58 |
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Re: AR88D gone low audio output
Thank you Martin.
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