UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Audio (record players, hi-fi etc)

Notices

Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

Reply
 
Thread Tools
Old 23rd Nov 2015, 8:37 pm   #61
Nickthedentist
Dekatron
 
Nickthedentist's Avatar
 
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 13,685
Default Re: Restore a Beau Decca

I'd connect one to each channel, and leave the third unconnected.

See which tapping on the amp works best.

You're right, leaving a valve amp's output unloaded is a bad idea.

N.
Nickthedentist is offline   Reply With Quote
Old 24th Nov 2015, 12:18 pm   #62
Edward Huggins
Dekatron
 
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 4,129
Default Re: Restore a Beau Decca

You could use 2 of the 3 speakers as the 2 stereo channels and leave the centre one unconnected. Then your output loading would be fine. The sound stage would just be a bit narrow. I suppose you could use the amp with 2 speakers on one of the channels, but this would affect the balance as it would present the wrong output impedence to that channel. Edward
Edward Huggins is offline   Reply With Quote
Old 24th Nov 2015, 4:06 pm   #63
AC/HL
Moderator
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 6,081
Default Re: Restore a Beau Decca

Surely, if you're using the original turntable and tuner, everything except the power amplifier is mono, so there's no stereo to consider. Just use one channel of the Rogers as it would have been with the missing amp.
__________________
Bill, BVWS member
AC/HL is offline   Reply With Quote
Old 24th Nov 2015, 4:09 pm   #64
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 9,872
Default Re: Restore a Beau Decca

Run two 7 Ohm speakers in series from the 15 Ohm output tap of one channel, and put a dummy load resistor on the other channel just to make sure it's happy. You only get the power of one channel but it ought to produce a reasonable sound.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 24th Nov 2015, 4:31 pm   #65
Nickthedentist
Dekatron
 
Nickthedentist's Avatar
 
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 13,685
Default Re: Restore a Beau Decca

There's no "right" answer, I suppose.

Personally, I would still be inclined to use one speaker per channel of the amp; you'd not have half the amp idling and doing nothing, you'd potentially get a greater total power output because you'd be using all of the amp rather than half of it, and you'd have the option of listening to an external source (CD player, iPod or whatever) in reasonable stereo.

N.
Nickthedentist is offline   Reply With Quote
Old 24th Nov 2015, 8:03 pm   #66
Techman
Octode
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 1,636
Default Re: Restore a Beau Decca

There really is only one correct answer to this question and that is as has been said, to connect one channel to one of the outer speakers and the other channel to the other outer speaker, leaving the middle one not connected. It’s a bad idea to leave one channel of the amplifier connected to a dummy load, as if a fault were to develop in this channel, you’d be unaware of it until the smoke started to rise! And talking of rising smoke, has that amplifier been serviced recently? The amplifier will need some inspection BEFORE any attempt is made to power it up. This may not be too much of a problem, as it will probably only require the replacement of 4 paper capacitors in each channel for safety and reliability at a cost of a fiver or so to you. There will be others, but these may not need replacing as they’re not in critical positions and the electrolytic smoothers may well prove to be fine.

Some things to keep in mind – don’t make the fitting of the amp too permanent, as an original type may turn up one day. The output from the Rogers amp may be a bit too powerful for those speakers individually – not a problem if you don’t run it flat out! If you’re worried about the power handling of the speakers, you could always put a bit of series resistance in line with each speaker and then some parallel resistance across the whole lot to adjust the impedance on each speaker. The resistors will need to be ‘watty’ types, values to be decided if you want to go down that path.

As a last thought – you could always electrically immobilise one of the amplifier channels – i.e., remove HT and heater supplies from one channel, but I think that this may be a task too far for you at this moment in time.
Techman is offline   Reply With Quote
Old 25th Nov 2015, 6:04 am   #67
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 6,531
Default Re: Restore a Beau Decca

The simplest method of avoiding damage would be to remove the output valves from the unused channel; note this may increase HT voltage, if the existing transformer has poor regulation. If this is a problem, increase the value of the smoothing resistor.
__________________
Julie {formerly known AJS_Derby}
julie_m is offline   Reply With Quote
Old 26th Nov 2015, 10:08 pm   #68
thejazzageuk
Pentode
 
Join Date: Feb 2014
Location: Narberth, Wales, UK.
Posts: 178
Default Re: Restore a Beau Decca

Again- thanks to everyone for their contribution. On considering all the posts I think I will opt to connect LH channel to LH speaker and RH to RH speaker- and leave the middle one unconnected.

Thanks to Techman regarding the AMP capacitors. I did a few basic checks but did power it up using a 'series lamp limiter' test lamp. No obvious problems. However I guess replacing the 4 paper caps could be a good idea. Here is a photo of the large caps- there are 2 100 microfarad ones and 2x 24+24 microfarad ones- do all 4 need to be replaced?- can they be checked to confirm if replacement is really required? Thanks
Attached Thumbnails
Click image for larger version

Name:	20151125_212732.jpg
Views:	140
Size:	68.0 KB
ID:	116112   Click image for larger version

Name:	20151125_212816.jpg
Views:	131
Size:	63.9 KB
ID:	116113  
thejazzageuk is offline   Reply With Quote
Old 27th Nov 2015, 12:14 am   #69
Techman
Octode
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 1,636
Default Re: Restore a Beau Decca

No, those four in the large silver cans are the ‘electrolytic’ types that I mentioned and are unlikely to need replacing, unless there’s either a problem with ‘hum’ regardless of volume setting, or they start to feel warm to the touch after a short while.

The ‘critical’ capacitors will be under the chassis, but I can see in the second picture a couple of ‘Mullard mustard’ type capacitors. These are very reliable and unlikely to cause any problems, but worth doing some voltage checks on the grids of the output valves just to be sure. I don’t know where those two capacitors I can see are in the circuit, but if the rest are the same type, then you probably won’t have any work to do other than a few voltage checks, which myself or other members can explain to you.

Pictures showing the complete underside of the chassis would be a good idea. A list of the valve types of the amplifier and also the valve type numbers of those in the tuner while you’re at it, would be very useful.

Last edited by Techman; 27th Nov 2015 at 12:22 am.
Techman is offline   Reply With Quote
Old 27th Nov 2015, 8:52 am   #70
thejazzageuk
Pentode
 
Join Date: Feb 2014
Location: Narberth, Wales, UK.
Posts: 178
Default Re: Restore a Beau Decca

Thanks Techman- that would certainly be a great help. I've attached a schematic plus component list and a photo of the underside.
Attached Thumbnails
Click image for larger version

Name:	20151127_073546.jpg
Views:	159
Size:	80.7 KB
ID:	116121  
Attached Files
File Type: pdf Rogers-Cadet-III-Schematic.pdf (1.29 MB, 86 views)
thejazzageuk is offline   Reply With Quote
Old 27th Nov 2015, 9:12 am   #71
Boater Sam
Dekatron
 
Boater Sam's Avatar
 
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,015
Default Re: Restore a Beau Decca

Look after those ECC807s!
__________________
Boater Sam.
BVWS Member
Boater Sam is offline   Reply With Quote
Old 28th Nov 2015, 2:37 pm   #72
Techman
Octode
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 1,636
Default Re: Restore a Beau Decca

That amp chassis looks to be in excellent condition, I’d go so far as saying that it’s unlikely to need any work doing whatsoever. For the perfectionist there may be one or two components that will be slightly out of tolerance due to age, but it probably wouldn’t be anything that you’d particularly notice and it’s probably a case of “if it ain’t broke, don’t fix it”!

It has ECL86 valves, I was expecting the EL84 for some reason. I think you’ll be fine driving a speaker on each channel without any resistors as padding with this one, but still don’t run it flat out. While on the subject of powering the speakers, you did realise that you should NEVER power up a valve amplifier without a load, ie, a speaker) connected? If you haven’t had any speakers connected and you’ve only had it powered on the lamp limiter, then you’ve probably got away with it. If you give it full power without a load/speaker connected to each output, then you risk destroying the output transformers which, due to expense, would write the amplifier off totally. You didn’t mention anything about what you had connected to it, so I thought I’d better mention it, just in case.

Correct me if I’m wrong, but is that the amp you bought from a forum member? It certainly looks to be in good condition and is probably actually better than the Decca one that would have been fitted originally. As said, when you power it up fully, make sure it’s connected to speakers and switch it off after couple of minutes and feel those electrolytic cans for any slight signs of warming. Keep doing this a number of times just to be sure and also check for any other signs of distress, although I suspect that it’ll all be fine. I think you’ve fallen on your feet with this one and hopefully you won’t ever have to replace those 807 pre-amp valves!
Techman is offline   Reply With Quote
Old 1st Dec 2015, 11:37 am   #73
thejazzageuk
Pentode
 
Join Date: Feb 2014
Location: Narberth, Wales, UK.
Posts: 178
Default Re: Restore a Beau Decca

Thanks Techman- It's good to know the Cadet appears to be in good condition-This is the Amp that Herald1360 kindly informed me about back in post 16.

I have been careful to connect speaker to the amp at all times.

I've checked the electrolytic cans and they don't get warm- so good news there. I have noticed however that the first ECC807 illuminates much brighter than the other two on start-up (pic enclosed). Is this a sign that some component could do with renewing?
Attached Thumbnails
Click image for larger version

Name:	20151130_183952.jpg
Views:	134
Size:	51.3 KB
ID:	116305  
thejazzageuk is offline   Reply With Quote
Old 1st Dec 2015, 1:23 pm   #74
ToneArm
Pentode
 
Join Date: Feb 2015
Location: Conwy, Clwyd, UK.
Posts: 179
Default Re: Restore a Beau Decca

Hi,
is it just a quick blink for a second or two when you first switch it on?

I've got a mullard ECC83 that does the same, and I'm told it's normal - some valves were designed to give a visual check or something. Apparently they're nicknamed flashers!
Glyn
ToneArm is offline   Reply With Quote
Old 1st Dec 2015, 4:10 pm   #75
AC/HL
Moderator
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 6,081
Default Re: Restore a Beau Decca

I've never heard of it being deliberate, just that the insulation between the heater and cathode stops a bit short, leaving exposed heater wire. Not uncommon.
__________________
Bill, BVWS member
AC/HL is offline   Reply With Quote
Old 7th Dec 2015, 8:17 pm   #76
thejazzageuk
Pentode
 
Join Date: Feb 2014
Location: Narberth, Wales, UK.
Posts: 178
Default Re: Restore a Beau Decca

Thanks all- so hopefully no need to do much to the amp.

Now for one of the more tricky decisions- how to operate the amp when installed in the cabinet. I've attached a couple of photos- one of the front of the amp, and one of the on/off volume.

As a minimum I would like to operate the on/off volume from the 'original' position. How to do this though? Positioning the amp pointing up/ using a mechanical link, or using a link harness are all possibilities- any suggestions welcome- especially if you have done something similar...
Attached Thumbnails
Click image for larger version

Name:	20151207_185242.jpg
Views:	140
Size:	55.3 KB
ID:	116568   Click image for larger version

Name:	20151207_183545.jpg
Views:	135
Size:	74.8 KB
ID:	116569  
thejazzageuk is offline   Reply With Quote
Old 8th Dec 2015, 12:35 pm   #77
Edward Huggins
Dekatron
 
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 4,129
Default Re: Restore a Beau Decca

Setting in the amp vertically so the control panel sits on to the horizontal board is best - BUT - this would/may mean your have to cut out more the original board and I would do nothing to affect the originality of the DECOLA cabinet. I would site the Rogers on a small plinth seperate to the main cabinet or set it into the back so you could get to the volume /on/ff easily. Edward
Edward Huggins is offline   Reply With Quote
Old 8th Dec 2015, 7:28 pm   #78
Techman
Octode
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 1,636
Default Re: Restore a Beau Decca

Unfortunately I have to agree with Edward that you've no real choice other than to mount the amp on its side. I don't like amps on their side. but the other option is to extend the control panel, and you can trust me when I tell you that you'll never do this and make it work properly in a month of Sundays. When I was a youngster, I build a radiogram (well actually it was just a gram in a homemade radiogram sized case) and mounted a homebrew Mullard 3-3 in the bottom of the case. I extended all the volume and tone controls to a plate in the top of the cabinet and spent ages sorting out instability causing HF oscillation and also hum pickup. I got it sorted in the end, but the difference was that I had a good idea of how to sort it, unfortunately I think it would be a bit beyond you skills at the moment and would also spoil a very good 'classic' amplifier.
Techman is offline   Reply With Quote
Old 8th Dec 2015, 9:09 pm   #79
Nickthedentist
Dekatron
 
Nickthedentist's Avatar
 
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 13,685
Default Re: Restore a Beau Decca

Some kind of Bowden-type cable, or even some flexible hose, to couple a knob to the volume pot?
Nickthedentist is offline   Reply With Quote
Old 8th Dec 2015, 9:23 pm   #80
TonyDuell
Nonode
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 2,289
Default Re: Restore a Beau Decca

About 40 years ago I remember seeing a flexible drive cable for 1/4" spindle controls in, IIRC, Home Radio (Mitcham). It was not cheap even then.

I wonder if a bit of car speedometer cable (OK, modern cars have electronic speedos but there must be plenty of cables still available, if only for classic car restorations) could be used. Or perhaps one of those cables used to give a flexible drive to an electric drill. Make up some couplers to link it to the pot spindle and the knob.
TonyDuell is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 2:42 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.