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 11th Sep 2019, 5:29 pm   #141
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,078
Default Re: Shaftesbury 519 amplifier

Picture in post #28 appears to show a 180 ohm cathode resistor (brown, grey, brown) in parallel with a capacitor wired from pin 3 to chassis.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now   Reply With Quote
Old 11th Sep 2019, 5:46 pm   #142
Guitarist28
Heptode
 
Guitarist28's Avatar
 
Join Date: Dec 2009
Location: Hockley, Essex, UK.
Posts: 556
Default Re: Shaftesbury 519 amplifier

Ok, I've now tried with my Epiphone 339 semi acoustic. The semi is acoustically louder than the amp even with the volume turned full up. It's very, very thin sounding and highly distorted (but not in a harmonic 'nice' way). The Tremelo does not work work (i'm aware that the switch changes the depth) but there is nothing.
Perhaps I was far too optimistic that this was going to be a great straight off the bat!!

I suppose the real work starts now.
Guitarist28 is offline   Reply With Quote
Old 11th Sep 2019, 5:49 pm   #143
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,078
Default Re: Shaftesbury 519 amplifier

You're nearly there!

Check the resistance of the cathode resistor with the power off. It may have drifted in value, or the bypass capacitor may be leaking, or the wrong way round if it's been replaced.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now   Reply With Quote
Old 11th Sep 2019, 5:57 pm   #144
Tim
Nonode
 
Tim's Avatar
 
Join Date: Jan 2003
Location: Bradford on Avon, Wiltshire, UK.
Posts: 2,731
Default Re: Shaftesbury 519 amplifier

If there is a screen grid resistor for the EL84, check that too. Screen supply might just be taken off the second HT capacitor, that is usually fed from the first section by a smoothing/dropping resistor.
Incidentally, with the amp on, volume up a bit and power on do you get a loud buzz when you touch the meter probe to the EL84 grid( pin2)?
__________________
"Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."
Tim is offline   Reply With Quote
Old 11th Sep 2019, 6:06 pm   #145
Guitarist28
Heptode
 
Guitarist28's Avatar
 
Join Date: Dec 2009
Location: Hockley, Essex, UK.
Posts: 556
Default Re: Shaftesbury 519 amplifier

If I am correct here I did not replace the electrolytic and resistor off pin 9 of the EL84. I'm not beginning to think I should replace all the electrolytics apart from the smoothing cap?
I will check the screen resistor and if all recall it had drifted slightly high but was well within a 20% limit.
Tim - yes indeed, there was a buzz at pin 2 (EL84 grid).
Do I need to be concerned about the tremolo side of things at present??
Guitarist28 is offline   Reply With Quote
Old 11th Sep 2019, 6:10 pm   #146
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,078
Default Re: Shaftesbury 519 amplifier

Please don't start replacing components because they might be faulty. Do as I suggest in post #144 and if the results are good check the cathode volts again.

Buzz at pin 2 is good, but it doesn't show that the EL84 is necessarily operating at its best.

Forget the tremolo for now.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now   Reply With Quote
Old 11th Sep 2019, 6:31 pm   #147
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,261
Default Re: Shaftesbury 519 amplifier

Quote:
Originally Posted by Guitarist28 View Post
Ok, I've now tried with my Epiphone 339 semi acoustic. The semi is acoustically louder than the amp even with the volume turned full up. It's very, very thin sounding and highly distorted (but not in a harmonic 'nice' way). The Tremelo does not work work (i'm aware that the switch changes the depth) but there is nothing.
Perhaps I was far too optimistic that this was going to be a great straight off the bat!!

I suppose the real work starts now.
First things first, EL84's cathode volts to sort out according to your measurement, touching g1 should produce a buzz from the loudspeaker once/if the EL84 stage and loudspeaker are working.

The stage before that is the first half of the ECC83, coupling to its grid is from the anode of the second half, the tremelo modulation is fed in at the grid of the first half and the tone control circuit is connected to the anode of the first half.

Inputs to the grid of the second half are via the volume controls.

So far as I can make out.

The coupling capacitor from the tremelo is a polystyrene/sufflex type, not saying it's faulty but I have known them to go leaky or short or open circuit from my servicing days so if it were mine I would replace it at some point.

Note: I wrote some of this before some of the previous post were posted so apologies for any duplicated suggestions etc.

Lawrence.

Last edited by ms660; 11th Sep 2019 at 6:42 pm. Reason: additional info
ms660 is online now   Reply With Quote
Old 11th Sep 2019, 6:34 pm   #148
Guitarist28
Heptode
 
Guitarist28's Avatar
 
Join Date: Dec 2009
Location: Hockley, Essex, UK.
Posts: 556
Default Re: Shaftesbury 519 amplifier

Ok, If referring to pin 3, then the resistor which should be 150R (10%) is in circuit at 160R so I would take that as being ok. The 25uF cap appears to be showing 330nF which cannot be a true value and is taken again in circuit, so I am thinking to disconnect and remeasure. Am I looking at the right components here?
Guitarist28 is offline   Reply With Quote
Old 11th Sep 2019, 6:40 pm   #149
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,078
Default Re: Shaftesbury 519 amplifier

You cannot measure that capacitor in circuit. The parallel resistor will make it appear leaky and spoil any measurement.

Check the cathode volts again. If it's still zero disconnect one end of the cap and see what the voltage is then.

If the resistor is coded brown, green, brown rather than brown, grey brown it's 150R rather than 180R.
Attached Thumbnails
Click image for larger version

Name:	chassis 1.jpg
Views:	16
Size:	30.5 KB
ID:	189994  
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now   Reply With Quote
Old 11th Sep 2019, 6:42 pm   #150
Tim
Nonode
 
Tim's Avatar
 
Join Date: Jan 2003
Location: Bradford on Avon, Wiltshire, UK.
Posts: 2,731
Default Re: Shaftesbury 519 amplifier

Yes. You only need to disconnect one end of the capacitor to test.

Just to confirm, your meter was set to DC when you measured the EL84 cathode voltage?
__________________
"Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."
Tim is offline   Reply With Quote
Old 11th Sep 2019, 6:53 pm   #151
Guitarist28
Heptode
 
Guitarist28's Avatar
 
Join Date: Dec 2009
Location: Hockley, Essex, UK.
Posts: 556
Default Re: Shaftesbury 519 amplifier

It’s definitely brown, green, brown and therefore 150R.
I can’t have got a good connection to pin 3 as I measured the underside of the pin this time around and it’s measured 7.1V DC
Guitarist28 is offline   Reply With Quote
Old 11th Sep 2019, 7:02 pm   #152
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,261
Default Re: Shaftesbury 519 amplifier

Quote:
Originally Posted by Guitarist28 View Post
It’s definitely brown, green, brown and therefore 150R.
I can’t have got a good connection to pin 3 as I measured the underside of the pin this time around and it’s measured 7.1V DC
Rob, I'll do a reverse engineered schematic as best as I can from the photo's for the main amp chassis tomorrow and post it in this thread, it might help you to find your way around.

Lawrence.

Last edited by ms660; 11th Sep 2019 at 7:07 pm.
ms660 is online now   Reply With Quote
Old 11th Sep 2019, 7:03 pm   #153
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,078
Default Re: Shaftesbury 519 amplifier

7.1VDC is much better.

Before moving on to the ECC83 I'd check the EL84's grid resistor (pin 2) and the screen grid resistor pin 9 if there is one, perhaps at the end of the red wire going to the right?
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now   Reply With Quote
Old 11th Sep 2019, 7:06 pm   #154
Guitarist28
Heptode
 
Guitarist28's Avatar
 
Join Date: Dec 2009
Location: Hockley, Essex, UK.
Posts: 556
Default Re: Shaftesbury 519 amplifier

I really cannot thank you all enough. I'm learning so much out of this and making great progress. I'm really pleased to be back on the forum again after such a long break.
I'm out for the rest of this evening and will be picking up again tomorrow.
Guitarist28 is offline   Reply With Quote
Old 11th Sep 2019, 8:08 pm   #155
Tim
Nonode
 
Tim's Avatar
 
Join Date: Jan 2003
Location: Bradford on Avon, Wiltshire, UK.
Posts: 2,731
Default Re: Shaftesbury 519 amplifier

That’s more like it! The EL84 is passing about 47mA cathode current. Allowing for screen grid current the Anode current is probably around 40mA, so seems OK. At least DC wise anyway.
__________________
"Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."
Tim is offline   Reply With Quote
Old 12th Sep 2019, 10:50 am   #156
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,261
Default Re: Shaftesbury 519 amplifier

As said, reverse engineered schematic for part of the Shaftesbury 519, based on photo's to date from this forum and other stuff on the web.

Guilty as charged if any errors.

Lawrence.
Attached Thumbnails
Click image for larger version

Name:	shaftesbury519amplifier.jpg
Views:	34
Size:	75.5 KB
ID:	190022  
ms660 is online now   Reply With Quote
Old 12th Sep 2019, 1:41 pm   #157
ITAM805
Octode
 
ITAM805's Avatar
 
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 1,693
Default Re: Shaftesbury 519 amplifier

Quote:
The semi is acoustically louder than the amp even with the volume turned full up. It's very, very thin sounding and highly distorted (but not in a harmonic 'nice' way).
Hi Rob, is the speaker in good order?
ITAM805 is offline   Reply With Quote
Old 13th Sep 2019, 6:54 am   #158
sparkymike
Hexode
 
Join Date: Dec 2006
Location: Colchester, Essex, UK.
Posts: 429
Default Re: Shaftesbury 519 amplifier

This amp looks very similar to an old guitar amp I have in the loft here, which I gave up on a long time ago.Now gathering dust !!
Believe that was made by a company known as RS, used to advertise in the 50/60,s radio mags.
Mike.
sparkymike is offline   Reply With Quote
Old 13th Sep 2019, 5:05 pm   #159
Guitarist28
Heptode
 
Guitarist28's Avatar
 
Join Date: Dec 2009
Location: Hockley, Essex, UK.
Posts: 556
Default Re: Shaftesbury 519 amplifier

For the EL84, the grid resistor (pin 2) should be 680kR and was actually 940kR!! I've replaced it and again because its out in the workshop, I could only test it quickly with a guitar lead and rubbing the end (I know this is not the best way to do this). Yes, it is louder but I still think it short of the mark.
The power resistor to pin 9 rated at 200R is measuring 209R so no problems there.
Additionally, I have noted that:
- volume control to the 2nd channel isnt working at he moment
- the EF86 has either blown or is not getting power as there is no filament glow

Any suggestions for putting a signal through the input rather than a guitar at this stage?
Guitarist28 is offline   Reply With Quote
Old 13th Sep 2019, 6:11 pm   #160
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,261
Default Re: Shaftesbury 519 amplifier

Quote:
Originally Posted by Guitarist28 View Post
I have noted that:
- volume control to the 2nd channel isnt working at he moment
- the EF86 has either blown or is not getting power as there is no filament glow

Any suggestions for putting a signal through the input rather than a guitar at this stage?
You can check both volume control circuits doing a buzz test, I've drawn the input sockets as switched to ground when no jack plug is inserted in the schematic I did because a picture of one on the web seemed to imply switched jack sockets, basically the signals from input 1 and input 2 end up at pin 2 of the ECC83, there's not a lot between the sockets and pin 2, just the pots, the 470k resistors and the wiring.

You could feed the output from a sig gen into the inputs or line out from whatever or possibly an MP3 player.

If you could do some photos of the front and the back of the EF86 panel with the valve removed it might be possible to reverse engineer that part of the circuit as well.

Lawrence.
ms660 is online now   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 9:45 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 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.