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

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 14th Jan 2019, 9:45 pm   #41
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Graves Vulcan

I think the PM2 should be the output valve (in the wrong socket?) and the PM1LF's should be the regen detector and AF amp valves.

Lawrence.
ms660 is offline  
Old 14th Jan 2019, 9:48 pm   #42
radiosoul
Tetrode
 
Join Date: May 2016
Location: Eastbourne, East Sussex, UK.
Posts: 68
Default Re: Graves Vulcan

..forgot to mention the the values of components shown in brackets are measured values.
radiosoul is offline  
Old 14th Jan 2019, 9:52 pm   #43
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Graves Vulcan

Quote:
Originally Posted by radiosoul View Post
..forgot to mention the the values of components shown in brackets are measured values.
Typical values for regen detector grid leak would be 200 or 300pF or thereabout and 2 megohms or thereabout….those values are not set in stone.

The data sheets for an idea for grid bias voltage/supply voltage....

PM1LF:

http://www.r-type.org/pdfs/pm1lf.pdf

PM2:

http://g3ynh.info/valves/old/Data-Bo...G/RVG-p011.pdf

Lawrence.

Last edited by ms660; 14th Jan 2019 at 10:09 pm. Reason: Links added
ms660 is offline  
Old 14th Jan 2019, 10:26 pm   #44
snowman_al
Octode
 
snowman_al's Avatar
 
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
Default Re: Graves Vulcan

Quote:
Originally Posted by ms660 View Post
The capacitance (capacitor) will be between the P & G connection I would imagine.
DOH I am so slow sometimes! You told us that yesterday.
Of course there is a capacitor in the Resistance Coupling Unit.

radiosoul, have you done a capacitance measurement from P to G in the RCC?
snowman_al is offline  
Old 14th Jan 2019, 11:35 pm   #45
radiosoul
Tetrode
 
Join Date: May 2016
Location: Eastbourne, East Sussex, UK.
Posts: 68
Default Re: Graves Vulcan

Just tuned in again. Not surprise to find the PM2 in the wrong place. With what ms660 has given us the PM2 should be the output valve so I'll relocate it there.

snowman-al, when you say P to G do you mean the capacitance across that "resistor" in the anode circuit of V1?

On that RC coupling board the glass enveloped "resistor" in the anode circuit of V1 has "P" marked on one side (connected to the swinging coil) and "+" marked on the side connected to HT+

Or are you looking at the grid of V2?
radiosoul is offline  
Old 15th Jan 2019, 1:04 am   #46
radiosoul
Tetrode
 
Join Date: May 2016
Location: Eastbourne, East Sussex, UK.
Posts: 68
Default Re: Graves Vulcan

OK. Went further into this. Photo attached. I did an analysis of the RC coupler baseboard and one measurement stood out. That was 228pF diagonally between the terminal marked "P" and that marked "G". This appears to confirm what you were saying snowman_al. So there is a hidden capacitor in the baseboard then!

All tests:

Diagonally across from "P" to "G"
Resistance:about 120 M Ohm but bouncing around and not stable. Assume no resistor here.
Capacitance 228 pF - stable

Between "P" and "+"
Resistance: 900M Ohm - assume no resistor
Capacitance: 1.6pF - very low - assume no capacitor

Between "-" and "G"
Resistance: 900M Ohm - assume no resistor
Capacitance: 3.7pF - very low - assume no capacitor

Between "-" and "+"
Resistance: 1.37 G Ohm Ohm - assume no resistor
Capacitance: 3.7pF - very low - assume no capacitor

So tests appear to have revealed a hidden capacitor in the RC unit. Does this sound right?
Attached Thumbnails
Click image for larger version

Name:	Ediswan RC unit baseboard.jpg
Views:	64
Size:	80.1 KB
ID:	176443  
radiosoul is offline  
Old 15th Jan 2019, 8:45 am   #47
snowman_al
Octode
 
snowman_al's Avatar
 
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
Default Re: Graves Vulcan

Yep,
there is a capacitor inside the Ediswan ''RC Unit'', just as ms660 said all along... That is the missing link connecting V1 to V2.

Apologies, but I have re-jigged the diagram and marked the RCU in a green box and noted the connection identifiers, + (HT), P (anode), G (grid) and - (grid bias).

Fathom out how V1 the detector works now then?
Attached Thumbnails
Click image for larger version

Name:	Vulcan3-001.jpg
Views:	103
Size:	46.1 KB
ID:	176460  
snowman_al is offline  
Old 15th Jan 2019, 6:46 pm   #48
radiosoul
Tetrode
 
Join Date: May 2016
Location: Eastbourne, East Sussex, UK.
Posts: 68
Default Re: Graves Vulcan

Hi snowman_al, thanks for the updated diagram! So we'll call that version 2! I'd marked up the diagram last night but didn't get around to sending it. It also had the P, G, + and - marked up. I haven't worked with those units before so I couldn't see that the capacitor was inside the unit and not external. I'll also start to mark up the components so that we know which is which. One thing I don't get is how any signal would get through that 228pF capacitor with that Dubilier 0.005uF capacitor which, in my view, would ground any signal variations at "P".
radiosoul is offline  
Old 15th Jan 2019, 6:54 pm   #49
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Graves Vulcan

Quote:
Originally Posted by radiosoul View Post
One thing I don't get is how any signal would get through that 228pF capacitor with that Dubilier 0.005uF capacitor which, in my view, would ground any signal variations at "P".
We can't be certain yet as to what the value of the built in capacitor should be, also double check the value (marked and measured) of that Dubilier 0.005uF.

Lawrence.
ms660 is offline  
Old 15th Jan 2019, 7:02 pm   #50
radiosoul
Tetrode
 
Join Date: May 2016
Location: Eastbourne, East Sussex, UK.
Posts: 68
Default Re: Graves Vulcan

Hi Lawrence, the Dubilier is marked at 0.005uF but measures as 0.00369uF. Just marking up version 3 of the diagram now following on from snowman-al's corrections..
radiosoul is offline  
Old 15th Jan 2019, 8:59 pm   #51
radiosoul
Tetrode
 
Join Date: May 2016
Location: Eastbourne, East Sussex, UK.
Posts: 68
Default Re: Graves Vulcan

OK folks, here's version 3 of the circuit diagram incorporating snowman_al's changes. Now I'm wondering if there's stuff hidden under the valve bases!

Probably time for me to get a decent circuit drawing package the does valves - suggestions welcome.

Anyway, I have named the components for consistency and those values in brackets are the measured values. I have put the PM2 in the output position.

Going back to post 32 by snowman_al, I can't see how the front end can work without his suggested grid leak resistor arrangement.

On the subject of C1 (the flat capacitor), the capacitance does go up to about 60pF if I compress it a bit so that seems to confirm PJL's post N° 34 that compression could bring the capacitance up toward a more realistic level. The state of the mica in the capacitor is not good and there seems to be some sort of glue residue in between the mica and the (brass?) plates that has deteriorated. It might be worthwhile checking the value of that capacitor in the the Vulcan II circuit diagram - I'll try to look that up.
Attached Files
File Type: pdf Graves Vulcan 3-Valve set - circuit diagram - v3.0.pdf (1.40 MB, 55 views)
radiosoul is offline  
Old 15th Jan 2019, 9:12 pm   #52
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Graves Vulcan

It's possible someone has fitted an RF RC coupling unit instead of an AF one, the 0.005uF in it's circuit position seems too high a value to me, I would expect less and also an RFC in the anode circuit with another filter capacitor, the grid of V1 clearly needs a leak resistance.

Here's a McMichael RC coupling unit, 0.005uF and an 80k anode load resistor:

https://www.americanradiohistory.com...ch=%22coupling unit%22

Lawrence.

Last edited by ms660; 15th Jan 2019 at 9:17 pm. Reason: Link added
ms660 is offline  
Old 16th Jan 2019, 12:09 am   #53
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
Default Re: Graves Vulcan

The capacitance and resistance values as shown should work but the audio bandwidth will be a bit limited with -3dB points at around 300 and 1600 c/s. Given the likely performance of period loudspeakers that wouldn't sound too bad, but taking the 0.005u down to 0.0022u and the 228p up to 470p wouldn't hurt.
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is online now  
Old 16th Jan 2019, 8:33 am   #54
snowman_al
Octode
 
snowman_al's Avatar
 
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
Default Re: Graves Vulcan

Quote:
Originally Posted by radiosoul View Post
... One thing I don't get is how any signal would get through that 228pF capacitor with that Dubilier 0.005uF capacitor which, in my view, would ground any signal variations at "P".
That cap is there to bypass any RF signals, that remain after detection, to ground. See it as a 'refinement' of sorts so the second valve only amplifies the AF signal.

As is pointed out the values you have sort of 'work', but are odd. I wonder what the cap in the RC unit was originally? Probably more than 228pF, but at least it is not leaky electrically.
snowman_al is offline  
Old 16th Jan 2019, 11:41 am   #55
snowman_al
Octode
 
snowman_al's Avatar
 
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
Default Re: Graves Vulcan

Looking at the diagram again, there may be another oddity as drawn.

I assume that normally battery sets with grid bias batteries are similar in that:
The HT -ve and LT-ve lines are joined or are the same line?
Then that the +ve grid bias is always (?) returned to the same HT/LT -ve line. Yes?

So as draw this set has the +ve grid bias connected to HT -ve via the valve filaments. (See ''Battery Connector Red'')

Sorry again, radiosoul, can you conform that the Red plug is not connected to the HT -ve line, but is as drawn?
Attached Thumbnails
Click image for larger version

Name:	Vulcan c-001.jpg
Views:	59
Size:	50.7 KB
ID:	176516  

Last edited by snowman_al; 16th Jan 2019 at 11:47 am.
snowman_al is offline  
Old 16th Jan 2019, 9:22 pm   #56
radiosoul
Tetrode
 
Join Date: May 2016
Location: Eastbourne, East Sussex, UK.
Posts: 68
Default Re: Graves Vulcan

Hi snowman_al and thank you to Herald 1360 for your comment on the capacitor.

Confirmed.

The red connector is connected only to one of the filament terminals on all three valves. The other filament terminals go to HT- through the battery switch. So the way I see it, Red Battery is LT+ and LT- would connect to HT-

Looking at that twisted pair lead at the bottom of the diagram, I'm wondering if it might have been used to connect an external battery which provided the filament supply. Perhaps the original battery pack was not used?
radiosoul is offline  
Old 16th Jan 2019, 9:49 pm   #57
snowman_al
Octode
 
snowman_al's Avatar
 
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
Default Re: Graves Vulcan

OK,
This set needs three batteries to work.
Yes 2 are external. 1 for LT and another for HT.
LT+ and LT- require a 2 volt accumulator to power the filaments.
HT+ and HT- use an HT battery (90 volts or so) to give the high voltage.
The internal one is a Grid Bias battery (9 volts, tapped at each 1.5 volt cell) for setting the V2 and V3 bias. The three flying leads inside the set connect to this.

As I said earlier, normally the Grid Bias positive lead connects to the HT negative line for good reason. It gives a predictable negative voltage.
But not if it is connected as in the diagram. I will ponder...
snowman_al is offline  
Old 17th Jan 2019, 9:32 pm   #58
radiosoul
Tetrode
 
Join Date: May 2016
Location: Eastbourne, East Sussex, UK.
Posts: 68
Default Re: Graves Vulcan

Circuit diagram v4.0 with the LT+ and LT- marked. Also added at the bottom right the external terminal on the box of the set marked "E"
Attached Files
File Type: pdf Graves Vulcan 3 Valve set - circuit diagram - v4.0.pdf (1.46 MB, 52 views)
radiosoul is offline  
Old 18th Jan 2019, 8:58 am   #59
snowman_al
Octode
 
snowman_al's Avatar
 
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
Default Re: Graves Vulcan

Hi radiosoul,
I think there is still some confusion about the three plugs, Red, Green and Black. They are the Grid Bias battery plugs, all of them will go to the Grid Bias battery.
The one you have marked LT+ve (Battery Connector Red) is not the LT+ connection.

As draw, the LT+ve connector is the 'Spade Connector'. The LT-ve will be the lead marked '?' and possibly had another spade connector in the past. The spades are typical for connection to a 2 volt accumulator. Have a
look here to see an example https://www.radiomuseum.org/r/ever_accumulator_gz.html

Apologies yet again, this is how I think it should be, with the grid bias red connection returned to the same line as the HT and LT negative connections.

I've also added a picture of a grid bias battery for info.

Getting there. Alan
Attached Thumbnails
Click image for larger version

Name:	grid bias.jpg
Views:	56
Size:	52.6 KB
ID:	176615   Click image for larger version

Name:	Bias Battery.jpg
Views:	68
Size:	151.9 KB
ID:	176616  
snowman_al is offline  
Old 18th Jan 2019, 10:19 am   #60
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
Default Re: Graves Vulcan

The only bit missing now is a grid leak for the detector, though it's possible the capacitor may be leaky enough. Apart from the RC coupling to the first AF stage, it now looks like a a bog standard late '20s 0-V-2 set.
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:58 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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.