KW Victor

[G3PIJpeter]

I have recently unearthed a brand-new Gelosos VFO (complete in its Italian cardboard box) with 6L6 driver capable of driving a pair of 807s or 6146s. I was planning to build a copy of the KW Vanguard transmitter around this VFO (adding the Top Band modification) for AM transmission on 160, 80 and 40 metres.
Since the VFO can drive a pair of PA valves, I am now planning to build a replica of the KW Victor that appeared briefly in adverts in early 1960s SWMs. It looked like a Vanguard but not quite, as I vaguely remember. However, the Web has absolutely nothing to say about this transmitter. I assume it was simply a beefed-up Vanguard with a pair of 6146s in the PA and the modulator uprated to a pair of 807s.
Does anyone have any details about the valve lineup or even a circuit diagram? If not, I suspect that the Victor never saw production and was an irrelevancy at that time of steady conversion of stations to SSB.
- Peter G3PIJ

[G4XWDJim]

Quite a few years ago when I was a keen member of the vmars net there was a G2 user with a Victor who had never converted over to SSB and just carried on using his AM gear. He lived in Weymouth I think.

I'm embarrassed to admit to forgetting his name but he was quite elderly. I think he appeared in an article in the newsletter together with some details of his TX.

Someone else will remember him I'm sure. If not I can search my old log books for his call sign. It's possible that the KW group will have info.

I built a lash up transmitter with a Geloso VFO I have using a pair of EL38s so that I could try suppressor grid mod but I blew the valves through trying too hard before I got anywhere with it. 100 watts was ok before they went S/C. I never progressed any farther and dismantled it some time later. The VFO was well capable though.

Jim

[Station X]

Forum member vosperd has posted the circuit on the KW yahoo group.

https://groups.yahoo.com/neo/groups/...tor%20copy.jpg

You may need to join the group to see it.

[Keith]

Hi Jim,

The station you are thinking of was Frank, G2XQ, a wonderful old gentleman, now sadly SK. I worked on his Victor on one occasion, the problem being the paxolin changeover switch arcing across from it's mains contacts! I must have obtained circuit information from somewhere, probably the KW group. Frank's TX is now in the hands of Mike, G1EDP, but he seems to have disappeared from the air. Another Victor that is still in use belongs to Don, M5AKY who is a member of this forum. The transmitter has been described as a Vanguard on steroids!

Good luck with the project Peter,

[vosperd]

Hi.
Yes, I do have a working Victor. I think there are at least four more around but not heard on the air very often. Not sure how many they made.
I'll attach the circuit diagram if it's not too big, otherwise I can send it direct.
Cheers
Don m5aky

[G4XWDJim]

Thanks Keith,

Of course. G2XQ, I had many QSOs with Frank and suspected that he would be SK. I think he was 92 when I used to work him about 10 years ago.

This arcing problem was common on Vanguards too and was a bad design feature. As the mains transformer was disconnected when going back to receive the back EMF would cause a splash down to the spindle of the Yaxley switch and eventually carbonise the switch. I modified several, my own two and Stuart's so that the Yaxley switch switched a low voltage relay and its contacts switched the mains. Good and reliable after that.

Jim

[G3PIJpeter]

Many thanks to all for your swift and useful replies. I have applied for membership of the KW group (lapsed when I retired from my work email address) and will download vosperd's (Don's?) circuit diagram. In the meantime, the thumbnail is perfectly readable and I can guess most of the component values.
Another question that springs to mind on looking at the circuit - how did KW get away with not using any form of PA neutralisation? The DX100 (2 x 6146) uses a pi-section coupler from the driver and so added capacitive loading to the PA grid - but the KW Vanguard and Victor use a simple capacitive feed from a high-impedance tuned circuit in the driver anode. Possibly, things are OK with the 6146 but not with the 6146B, which is an entirely different sort of bottle.
Anyhow, I expect that propagation supporting 28 Mc/s AM will be well in the past by the time I finally lay down the soldering iron on this project - an non-neutralised PA should be OK on the LF bands.
73 - Peter

[vosperd]

I don't have any other info on the Victor so whilst we are on the subject I wonder if anyone has any info or ideas on the setting of the two pots R10 and R44. These pots are not on the Vanguard which has a similar overall circuit.
As the Victor has a negative bias supply is the clamp valve working in the same way as the Vanguard?
Don m5aky

[HamishBoxer]

That is a great find Peter I certainly remember that name from my swl days.

[G3VKM_Roger]

Originally Posted by G3PIJpeter

Many thanks to all for your swift and useful replies. I have applied for membership of the KW group (lapsed when I retired from my work email address) and will download vosperd's (Don's?) circuit diagram. In the meantime, the thumbnail is perfectly readable and I can guess most of the component values.

Hi Peter,

I OKed your KW_Radios group membership this morning so it should be active now.

David/G0SKE in Suffolk had a Victor too, back in 2007, a photo is attached. Not sure if he uses this group, though. Good luck with the project.

73

Roger/G3VKM

[Aub]

Originally Posted by G3PIJpeter

- how did KW get away with not using any form of PA neutralisation?

Hi Peter,

My homebrew AM Tx, for 160/80/40, uses 2 x 6146 in the PA. I can't remember if they are the B variety or not. As far as I know, it doesn't suffer any ill effects from not having neutralisation.

Good luck.

73, Aubrey G4KQL

[G3PIJpeter]

Originally Posted by G3VKM_Roger

I OKed your KW_Radios group membership this morning so it should be active now.
David/G0SKE in Suffolk had a Victor too, back in 2007, a photo is attached. Not sure if he uses this group, though. Good luck with the project.

Many thanks Roger - I have downloaded the circuit diagrams which are clearer than the thumbnail posted earlier here.

The front panel of David's Victor looks exactly the same as the Vanguard. I understand that the cabinet was a couple of inches deeper though. Is that a Radiovision 'Commander' RX?

The only spare modulation transformers here are from a TCS TX (too small) and a rather huge Woden UM3. The mains transformer collection has thrown up some very capable but large Admiralty specimens, so the PSU/mod may well end up in a separate case - but I am keen to produce a decent copy of the Victor front panel.

Aubrey - your homebrew 2 x 6146 is instructive - the LG300 uses a non-neutralised 813 so I suspect that all we need to do is maintain good layout and low-impedance earthing back to the cathode.

73 to all - Peter

[G3VKM_Roger]

Originally Posted by G3PIJpeter

Is that a Radiovision 'Commander' RX?

Yes, Peter, a Radiovision Commander it is. David has a habit of finding less common equipment! I think you're correct that the Victor cabinet was slightly larger than the Vanguard.

73

Roger

[Radio Wrangler]

Modulation transformers need to be a bit bigger than you'd expect for the power because they can't always cancel the DC current components, for example with a push-pull modulator where the DC components of the two audio valves act to cancel each other, but leave the DC component in the PA winding unchecked. So the core needs to be large enough to avoid saturation and to have enough inductance left if gapped.

That Woden UM3 should work nicely with a pair of KT88 modulating an 813 - such as an LG300 and its outboard modulator. Too big a mod transformer is OK, but too small is a disaster.

David

[Aub]

You could use an audio choke in the PA anode circuit HT feed, and then connect one side of the secondary of the mod. transformer to the top of the pa RF choke, via a capacitor. The other side of the mod. transformer secondary goes to earth. This method avoids the standing current the mod transformer secondary.

I considered doing this when i built my rig, but I didn't have a suitable audio choke, so stuck with the usual method. Incidentally, I have used mains transformers as mod. transformers with good results.

73s

Aub

[G6Tanuki]

You can indeed use mains transformers as modulation transformers: though as has been noted the standing DC of the RF PA can cause core-saturation issues. Pedants would de-stack the E and I core laminations and reassemble with an airgap; more prosaically, a larger-than-absolutely-needed transformer will "let you get away with it".

More than once I've used a big push-pull output transformer [dual-6L6/KT66-type] as a modulation transformer, with the PA [807] being connected to the anode of one of the push-pull valves. OK, less than ideal in terms of balance - and assumes the RF and audio valves need similar HT voltages, - but perfectly good enough for brewing up 30 or so Watts of "Communications quality" speech.

My other trick is using a mains-transformer HT secondary as a centre-tapped modulation-choke: HT to centre-tap, RF PA to one end, modulator-valve to the other. The DC anode-currents to the 2 valves being roughly equivalent, they don't generate any core saturation, and the anode impedance of an 807 is about the same whether running in Class-A or Class-C . Only downside is that you have to run the modulator in Class-A which tends to be horribly hungry on the old milliamps.

[G3PIJpeter]

Originally Posted by G6Tanuki

My other trick is using a mains-transformer HT secondary as a centre-tapped modulation-choke: HT to centre-tap, RF PA to one end, modulator-valve to the other.

This arrangement is straightforward 'Heising modulation' as used in the Codar TX.
Using a modulation choke with push-pull modulation transformer certainly removes the standing PA current from the secondary (see attached). I wonder if you can get away with using a smaller mod transformer with this arrangement e.g. a TCS TX transformer with 2 x AB2 807s into 2 x 6146? It would only have to handle peak audio power - peak power handling might be increased due to lack core magnetisation from PA current.
- Peter

[G3PIJpeter]

Originally Posted by Aub

You could use an audio choke in the PA anode circuit HT feed, and then connect one side of the secondary of the mod. transformer to the top of the pa RF choke, via a capacitor. The other side of the mod. transformer secondary goes to earth. This method avoids the standing current the mod transformer secondary.

The article at
http://www.amwindow.org/tech/pdf/art13shuntfed.pdf
indicates that I should be able to use the TCS mod transformer in a Victor line-up (2 x 807s producing around 80 watts of audio into 2 x 6146 (non-neutralised!) so long as the shunt-fed arrangement is used. With all the PA standing current going through the choke, it seems the mod transformer can stand a lot more audio than you would expect with the usual arrangement.
- Peter

[Keith]

Originally Posted by G4XWDJim

Of course. G2XQ, I had many QSOs with Frank and suspected that he would be SK. I think he was 92 when I used to work him about 10 years ago.

Jim,

Here is a picture of Frank with his Victor. There is a delightful interview with him at https://www.youtube.com/watch?v=mWaZQQ2rXm0

[Radio Wrangler]

'Communications quality' helps a lot, because if you cut off the audio below 300Hz a transformer doesn't need as much inductance as it would for hifi.

David