Graves Vulcan - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

radiosoul · 20th Jan 2019, 6:57 pm

Hi folks

Trying to switch between this forum (something I really like) and work (something I need to do)..

snowman_al, no apologies required, all suggestions most welcome and in fact that's getting me to put down the battery polarities on the diagram which I'll do next and post a bit later. Herald1360, the grid leak for the detector is what I'm poring over too.

Just to be sure, my take is that V1 is simply an RF amplifier and V2 is the detector. V3 being the audio amp. OK so far?

I had a visitor today who is into older model restoration and I'll put his suggestions for battery polarities on the diagram. Also suggested was another path for the regeneration via the second PM1 anode circuit but I'll submit that as another diagram. The same person confirmed my drawing by inspection of the set which was reassuring!

Working on it..

ms660 · 20th Jan 2019, 7:06 pm

Quote:

Originally Posted by radiosoul

Just to be sure, my take is that V1 is simply an RF amplifier and V2 is the detector. V3 being the audio amp. OK so far?

V1 is the detector....well it would be with a grid leak resistor.

Lawrence.

radiosoul · 20th Jan 2019, 9:56 pm

Take II.

I was off at a tangent perhaps.

So, if I look properly at the old radio theory books I've pulled out of a tight corner, then V1 is the detector using grid rectification such that amplified LF and HF will be presented at V1 anode. HF would, I expect, be filtered out by C3 leaving LF to pass to V2. Amplified signal positive feedback is applied with swinging coil L3.

All this, provided we have some sort of grid leak resistor across C2 or between grid and earth which we don't find in this set.

V2 must be the 1st AF amp and V2 the final.

Herald1360 · 20th Jan 2019, 10:33 pm

That's how I would see it. And it's what 0-V-2 means.....

0 RF stages
V Detector stage
2 Two audio stages.

Never seen a typical superhet described as a 0-V-1-V-2 though

radiosoul · 9th Feb 2019, 2:44 pm

Hi folks,

Been away for a while and away next week. The day job is getting in the way of radio but it's the income, you see.

After a chat with one or two people the thought was that V1 is simply an amp. But if I consider C4 and R2 as a potential divider then at, say, 1000Hz the reactance of C4 would be about 700kOhm which is small compared with R2 so no problem passing to V2 - most of the voltage would be across R2. Also, at 500kHz, C3 presents a reactance of 63 Ohm, rather small, so most of the RF would be bypassed by C3.

It looks as though I'll need to do some experimentation and try adding a grid leak resistor to V1.

20th Jan 2019, 6:57 pm	#61
radiosoul Tetrode Join Date: May 2016 Location: Eastbourne, East Sussex, UK. Posts: 68	Re: Graves Vulcan Hi folks Trying to switch between this forum (something I really like) and work (something I need to do).. snowman_al, no apologies required, all suggestions most welcome and in fact that's getting me to put down the battery polarities on the diagram which I'll do next and post a bit later. Herald1360, the grid leak for the detector is what I'm poring over too. Just to be sure, my take is that V1 is simply an RF amplifier and V2 is the detector. V3 being the audio amp. OK so far? I had a visitor today who is into older model restoration and I'll put his suggestions for battery polarities on the diagram. Also suggested was another path for the regeneration via the second PM1 anode circuit but I'll submit that as another diagram. The same person confirmed my drawing by inspection of the set which was reassuring! Working on it..

20th Jan 2019, 9:56 pm	#63
radiosoul Tetrode Join Date: May 2016 Location: Eastbourne, East Sussex, UK. Posts: 68	Re: Graves Vulcan Take II. I was off at a tangent perhaps. So, if I look properly at the old radio theory books I've pulled out of a tight corner, then V1 is the detector using grid rectification such that amplified LF and HF will be presented at V1 anode. HF would, I expect, be filtered out by C3 leaving LF to pass to V2. Amplified signal positive feedback is applied with swinging coil L3. All this, provided we have some sort of grid leak resistor across C2 or between grid and earth which we don't find in this set. V2 must be the 1st AF amp and V2 the final.

20th Jan 2019, 10:33 pm	#64
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: Graves Vulcan That's how I would see it. And it's what 0-V-2 means..... 0 RF stages V Detector stage 2 Two audio stages. Never seen a typical superhet described as a 0-V-1-V-2 though __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

9th Feb 2019, 2:44 pm	#65
radiosoul Tetrode Join Date: May 2016 Location: Eastbourne, East Sussex, UK. Posts: 68	Re: Graves Vulcan Hi folks, Been away for a while and away next week. The day job is getting in the way of radio but it's the income, you see. After a chat with one or two people the thought was that V1 is simply an amp. But if I consider C4 and R2 as a potential divider then at, say, 1000Hz the reactance of C4 would be about 700kOhm which is small compared with R2 so no problem passing to V2 - most of the voltage would be across R2. Also, at 500kHz, C3 presents a reactance of 63 Ohm, rather small, so most of the RF would be bypassed by C3. It looks as though I'll need to do some experimentation and try adding a grid leak resistor to V1.