18th Mar 2017, 12:12 pm | #221 |
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Re: Restore a Beau Decca
Looks good except for one measurement. The voltage across R36 is 41.5V but across R39 is 371-279=92V but these resistors are the same value and should be passing the same current. Try measuring the voltage across R39. If its still much greater than 41.5V, do you have a replacement for V8 (L63) as it might be heater cathode leakage?
Most importantly, is it still distorted and humming? Last edited by PJL; 18th Mar 2017 at 12:18 pm. |
19th Mar 2017, 1:29 pm | #222 |
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Re: Restore a Beau Decca
Thank you PJL.
You are correct, I've re-measured and the voltage across these resistors is almost the same. I think you mean R38 and R39 (the diagram is not at all clear between R36 and R38). The sound is very good now. There is no noticeable hum in gram positions 2 and 4, but there is a moderate level of hum in position 3 (via C41?). Also I do notice some distortion (like wind over a microphone). I will try to clean the valve pins to see if this reduces the noise- also the amp is on its side so putting it upright may help. |
19th Mar 2017, 1:49 pm | #223 |
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Re: Restore a Beau Decca
It's hard to say. It could be down to an open circuit. C41 is a type of capacitor that's unlikely to cause trouble in respect of leakage, but it's just possible that it's gone open circuit where the wires connect to the foil, which can happen with this type.
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19th Mar 2017, 3:06 pm | #224 |
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Re: Restore a Beau Decca
You are confident it is this switch position as C41 is just changing the tone by adding a parallel capacitor across the volume control.
I would clean the switch very thoroughly as it might be leakage in the switch wafer. Another possibility is the heater wiring is too close to the capacitor or wiring or there is an issue with the earthing point to the chassis. Do you mean hiss (present all the time in the background) or distortion (occurs only when there is a signal)? If its hiss then does it change with volume? If it changes with volume it would be worth changing the resistors around V1, particularly R27 and R24 for modern metal film types. Pentodes are always a bit noisy and this design has V1 running flat out so I doubt you will be able to get rid of it altogether. Good to hear it is working OK. |
19th Mar 2017, 3:38 pm | #225 |
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Re: Restore a Beau Decca
It does sound like an open circuit. This switch position also grounds pin 5 of the 'octal', so you could check with your meter that it's actually doing so in this position.
Remember what i said in a previous post with regards to those anode load resistors causing noise regardless of volume setting, so as said, you need to make it clear as to whether the 'wind' fault is volume setting related or not. I've had this problem and tapping them gently with a WELL INSULATED screw driver handle can sometimes provoke/alter the fault. You may even see one of them 'sparkling' in a darkened room, but first we need to establish whether the fault is before or after the volume control - it's ALWAYS important to make that clear. Edit to say - clean the switch contacts with Servisol 10 and meter them for proper continuity in any suspect positions. Last edited by Techman; 19th Mar 2017 at 3:47 pm. Reason: Extra info and typo. |
28th Mar 2017, 7:07 pm | #226 |
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Re: Restore a Beau Decca
I've cleaned the 'octal' and the valve bases/ pins. I'm pleased to say that everything now appears to be good.
All three positions on the 'octal' brilliance work as expected, and NO HUM on any position. So I am just giving it a good listening too before installing it into the cabinet. All I will do now is replace the mains cable with a new 3 amp one and install suitable mains caps- unless there is anything else I should do whilst it is accessible?.. Now starting to think about the next job - which will be to check out and get its radio unit working- I guess I need to make or get hold of the 'extension lead' to connect/power it up (which unfortunately was not present when I received it). |
31st Mar 2017, 10:01 am | #227 |
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Re: Restore a Beau Decca
The AMP is now performing well so I'm continuing to listen to it over the next few days.
During this I though I'd have a look at the radio unit. I've attached some photos to this post and would welcome any comments of suggestions how to proceed. I'm not even sure how to power it up as the 8 way connector on the back looks like nothing I've seen! |
31st Mar 2017, 10:52 am | #228 |
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Re: Restore a Beau Decca
Before you attempt to power it up, do clean all of the valve pins and top caps and the holders. I assume you do not have the female connector?
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Edward. |
31st Mar 2017, 2:10 pm | #229 |
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Re: Restore a Beau Decca
I actually thought that the second gram you got was actually complete so I am surprised to hear that the interconnecting lead is missing. You'll have to carefully make one up. The plug and socket are 'octal', which just to clarify, is what I was referring to when I mentioned the 'octal' in a previous post, rather than referring to octal valve bases. So there lies the clue - it's an 'octal' similar to a valve base. Be aware that there are two different standards and you'll need to know which one you've got but you can make a start by checking it against one of your existing octal valves and get a plug and socket of the same type. Someone else may know the exact octal standard used for this connector. For a quick and easy lash up you can then use an old valve base and socket. You'll need to be EXTREMELY careful when making up the lead that you get ALL the connections exactly right - check, check and check again before applying power!
Very well done getting the amplifier working. It certainly needed a bit more attention than at first thought, but it certainly could have been a lot worse. None of the repairs that have been done are irreversible, so you can always return to it at your leisure and replace any of the replacement components with more 'cosmetically' suitable examples should you want to. It may well turn out that the radio unit will need nothing more than switch and valve base cleaning as said by Edward. What I would advise is that using the knowledge that you've gained from the work you've done on the amplifier, that you study the circuit diagram and check for any of the 'paper' type coupling capacitors that would seem to have voltages derived from the HT line directly on one side of them for possible replacement before powering up. I don't have a circuit for this unit myself but there may be a small amplification stage just after the detector, which is probably the only part of the circuit to worry about in this regard. This stage will be just before the audio is taken to a pin connection on that 'octal' plug to be fed to the amplifier. When you make up a connecting lead, this audio connection will need to be made of screened cable. I'm assuming that there isn't a separate audio connection between the two units. |
1st Apr 2017, 9:56 am | #230 |
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Re: Restore a Beau Decca
Thanks Techman and Edward Huggins.
The Beau Decca I purchased was complete- but, believe it or not, the radio was not a standard fit on this gram, but an optional extra! The standard gram, which I have, had this blanking plate (photo) where the radio sits. I purchased the radio separately but it came without the connecting lead. I've had a quick look at octal connectors- the amp end looks to be easily available, but the radio end has that large blade connector in the middle and appears to be much harder to get hold of. Last edited by thejazzageuk; 1st Apr 2017 at 10:04 am. |
1st Apr 2017, 10:05 am | #231 |
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Re: Restore a Beau Decca
A picture of that connector on the radio end please, I'm sure I have made one of these from something else many years ago.
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1st Apr 2017, 10:28 am | #232 |
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Re: Restore a Beau Decca
Thanks Boater Sam
Here are photos of both ends that the lead will need to plug into. The radio is the one with the blade in the middle. |
1st Apr 2017, 10:33 am | #233 |
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Re: Restore a Beau Decca
I think the one with the blade might be Cinch.
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1st Apr 2017, 3:19 pm | #234 |
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Re: Restore a Beau Decca
Have you tried to (carefully) fit a normal octal valveholder onto that plug, with the stepped end of the 'blade' going into the keyway? I remember having a similar cable-mounted plug on some device that would go into a chassis-mouted octal valveholder.
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4th Apr 2017, 2:10 pm | #235 |
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Re: Restore a Beau Decca
Thanks for the suggestion. I have found this on on ebay (photo) that I will buy and see if it can be adapted to fit until a better solution can be found. Will let you know when it arrives if it will fit.
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4th Apr 2017, 2:26 pm | #236 |
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Re: Restore a Beau Decca
As far as I can remember, either an Octal or Mazda Octal socket fits if you cut a way in the socket for the blade. The pin spacing is different on these two sockets.
I may be wrong, its been a while. |
4th Apr 2017, 3:08 pm | #237 |
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Re: Restore a Beau Decca
You need to recap it before applying power, the original capacitors are grounded via the nut on the bottom, in other words there is only one terminal, the can and its screw thread are the other.
I carefully cut the can open, pull out the innards and restuff, I drill a small hole in the base for the ground wire to come out and then fit it all back together. |
6th Apr 2017, 12:25 pm | #238 |
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Re: Restore a Beau Decca
Though it looks as though it won't fit, that bladed plug and socket is just an Octal. I have found the same one on a Ferguson 289 radio, for the power supply.
Sam. |
7th Apr 2017, 12:35 pm | #239 |
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Re: Restore a Beau Decca
Thanks Boater sam- I have ordered on- will see if is possible to adapt it to fit then!
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7th Apr 2017, 12:49 pm | #240 | |
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Re: Restore a Beau Decca
Quote:
It will be a couple of weeks before I can power it up if I make up a connecting lead to do this. |
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