KW Victor

[G3VKM_Roger]

Originally Posted by Keith

Here is a picture of Frank with his Victor.

Interesting. From Keith's photo and that of the G0SKE's Victor that I posted, it looks like KW put a engraved nameplate on the Victor front panel, something they didn't do on other contemporary radios like the Viceroy, Vanguard, Valiant and KW-160. Maybe it covered-up some Vanguard markings, given the similarity between the two radios?

Does anyone know who acquired Frank's Victor? Looks like he was using a carbon mic with it.

73

Roger/G3VKM

[vosperd]

There is a black plastic engraved plate on the front of my Victor. Underneath it says "Vanguard"
I have the older style case and my front panel has not survived as well as Frank's
Don

[G3VKM_Roger]

Hi Don,

That says to me that the production run was low. Must look the Victor up in my SWM collection and see when it was introduced, any ideas of year?

73

Roger

[vosperd]

In Peter's original post he mentions SWM early 60's.
Don

[G3VKM_Roger]

Pretty close, the earliest I can find a mention of the Victor in Short Wave Magazine is November 1959, at which time the adverts cease to mention an SSB TX called the "Viscount". Has anyone ever seen one of those?

73

Roger/G3VKM

[vosperd]

http://www.leowood.net:88/amateurrad...teurradio8.htm

There is some info here if you do a word search for Viscount.

Can't say that I've heard of it before though. Is there any technical info on the Victor like there is for the Valiant in SWM?

[G3PIJpeter]

Originally Posted by vosperd

I wonder if anyone has any info or ideas on the setting of the two pots R10 and R44.

A pot in the grid of the clamp valve can be used as a power control - but the bottom end is usually returned to earth. The bottom of R10 in the Victor is connected to the half-HT point on the PSU smoothing capacitors (+350V?). The bottom of the RFC (L12) in the grid of the PA is connected to the top of the pot R10 and this junction is returned to the bias supply via R17 - so the pot has a negative potential applied to the top and a positive potential applied to the bottom.

So the question arises - what is the potential on the slider at different settings? The cathode of the 6AQ5 clamper is grounded and would not take kindly to a positive potential on its grid when the pot wiper was at the 'PSU HT end'.

R44 sets the negative bias on the PA grid (and at the top of R10). The bias supply looks fairly low impedance so extra 'grid leak' PA bias during drive will not amount to much. So - if the PA is being operated on fixed bias, why does it need a clamp valve - its only function seems to be as a power control?

My reasoning may well be faulty, but there's certainly something weird here. The answer is to build the thing and see what happens - however, no similar pre-switchon fears as with the Hadron Collider forming an earth-swallowing black hole.

- Peter

[G3VKM_Roger]

Originally Posted by vosperd

There is some info here if you do a word search for Viscount.

Thanks. I've not seen any info on the Viscount in my SWM collection, although there are a few gaps. I note from your link that the Viscount was also called the KW-500, which is confusing as the KW-500 I used to own was a linear amplifier with an 813 PA valve. The list mentions the Viscount as having a phasing-method sideband generator, so it wasn't a Viceroy clone. They did the same with the KW-160 Top Band TX, the type number was reused for a Top Band ATU.


Cheers

Roger

[G3VKM_Roger]

A further rummage through 1959 SWMs appears to show the Viscount as a possible never-wozzer and even some confusion over its model number, one advert calls it the KW-600, others the KW-500, the 600 was again a number reused later for a linear amp.

73

Roger

[G3PIJpeter]

Originally Posted by G3VKM_Roger

Thanks. I've not seen any info on the Viscount in my SWM collection, although there are a few gaps. I note from your link that the Viscount was also called the KW-500, which is confusing as the KW-500 I used to own was a linear amplifier with an 813 PA valve.

Pictures here
http://www.mods.dk/picture.php?brandid=49&model=kw-500
PSU clearly monster transformer with 866 mercury vapour rectifiers and an 813 in the PA. I wonder if you had to supply your own 813 as with the LG300?

I think the Victor power level is just about right when you consider the number of dB in doubling power output and the number of dB in an S-point - so I shall stick to a pair of 6146s. The Vanguard puts out only 30 watts or so due to HT being around 400 volts; the Victor should manage 100 watts output at least at 650 volts for AM service (2 x 650 x 0.12 = 156 watts input), a bit more at 750 V and CW if 6146Bs used.

- Peter

[G3PIJpeter]

I've now progressed this project to the point where I have the Geloso VFO (with modifications for Top Band) plus a 2 x 807 PA mounted behind a KW Victor sized front panel. I have chosen 807s over 6146s because I think there should be less likelihood of needing to neutralise them.
I'm now back to the problem of the modulation transformer and the question is - will a shunt-fed (see thumbnail) TCS mod transformer be OK or will it melt?
The spec from the TCS handbook is 6000 ohm CT primary and 6000 ohm secondary rated at 20 watts. Both primary and secondary are wound with no. 33 AWG enamel wire, which is rated at 0.43 A for chassis wiring, 72 mA for 'power transmission' and 2 A derated by 0.5 for bundling i.e. 1 A. The standing current for 6146Bs in AB1 push-pull is 48 mA at 650 V. For 70 W of audio output, the peak Ia will be around 160 mA. With the shunt choke taking all the DC to the PA anodes, will the TCS mod transformer stand these projected peak currents? It looks to be well capable of taking the idling (zero-signal) current of the 6146 modulator valves.
. . . and could a centre-tapped mains transformer be used in this arrangement with the 230 V primary feeding the PA via the shunt choke?
All thoughts as usual gratefully received - although this one may well end up as a 'Suck it and see'.
73 - Peter

[Sean Williams]

Peter, I have some ex ILS modulation transformers, that are much bigger than the TCS mod iron - would one of these be worth a go?

[G3PIJpeter]

ILS = Instrument Landing Systems? Transformer looks interesting so long as it is physically smaller than the spare UM3 I have here which is too big to fit in the Victor lookalike project.
Do you have any info on the electrical properties of your ILS transformer? Push-pull primary? Impedances? How were they originally used? What modulator and PA valves?
Many thanks for this lead.
- Peter

[m0cemdave]

I wouldn't like to operate a TCS mod transformer at KW Victor audio levels.

You could look out for an ART-13 type instead. It's about the same size and appearance as the TCS one but handles a lot more power - I think it has an improved type of core. It was designed for nominal impedances of 15k P-P to 7k3, i.e a turns ratio of 1.43 to 1.

There's also the Ferranti RD1736. This was for 2 x 807 (as Class B triodes) to 2 x 807, with a ratio of 2:1. Size is intermediate between the TCS and the UM3.

Both of these turn up regularly at rallies.

[G3PIJpeter]

Originally Posted by m0cemdave

I wouldn't like to operate a TCS mod transformer at KW Victor audio levels.

Certainly not with the PA current going through the secondary - but what about the shunt-fed arrangement? This circuit used to crop up in 1950s SWM QRO transmitter designs and it was obviously done for a reason, even when used with Woden modulation transformers.
- Peter

[Sean Williams]

Hi Peter,

I know the modulator was a push pull pair of 807s - from memory modulating a twin tetrode at VHF - around 70watts RF from memory - the modulator PSU transformer delivered 700-0-700 at about 300ma.....

I also have a Mod transformer from an ART-13 here too - that was a pair of 811s driving an 813 - that owes me a few quid though

Sadly no other info - wonder if you are going to Stockwood Park - I could chuck them both in the van with me

[G3PIJpeter]

Originally Posted by Sean Williams

I know the modulator was a push pull pair of 807s - from memory modulating a twin tetrode at VHF - around 70watts RF from memory - the modulator PSU transformer delivered 700-0-700 at about 300ma

Sean -
Looks like a QQVO-640A working in AM service with 600 volts at 200 mA = 120 watts in and around 70 out - so the modulating impedance should be similar to a pair of 807s or 6146s in the PA. I'm not going to the rally (now out of circulation working until early July) so I shall put a note in the diary to PM you then to arrange alternative means of delivery. Diesel from here to you would be about the same as postage! That transformer will certainly be beefy enough, especially if used with a shunt modulation choke. The TCS transformer impedances are less than ideal too.
Many thanks
- Peter

[BobGreen]

As a SWL in the 1950s, with my R107, it seemed that every (homebrew) station used a Geloso VFO and a pair of 807s plus another pair (or 6V6s) in the modulator. I remember hearing a few "Donald Duck" stations and was shown how to resolve them with the BFO. The early days of SSB!

[G3PIJpeter]

Originally Posted by vosperd

... 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?

I think I have found the answer to this one. The DX100 has a similar circuit around the grids of the PA valves with a 6AQ5 clamper. The construction manual has the following to say:
"The fixed bias applied to the grids of the 6146 stage would normally keep the 6AQ5 cut off also, regardless of loss of excitation. Consequently, a sufficient positive voltage is applied to the 6AQ5 grid to just balance the fixed bias but not the operating bias. This allows the clamp valve to be cut off by the operating bias only."
So the two pots in the Victor R10 and R44 are to set the levels of the standing negative bias on the 6146 grids and the positive bias that ensures the clamper conducts when excitation is removed.
So - that's sorted that one - until someone else comes up with a better idea!
- Peter

[G3PIJpeter]

The KW Victor clone is slowly being put together. There is now 8-10 mA of grid drive to the 2x6146A PA valves on all bands 160 to 10 metres.

Before firing up the PA, I would welcome thoughts on what sort of anode blocking capacitor to use. I need about 1000 pF and have fitted two paralleled ceramic capacitors labelled 560 pF 4000V. I also have a mica capacitor labelled 0.001 mFd at 2500 VDC working (see attached pics).

Which would be the best to use? I am not sure about their relative abilities to handle the RF current involved.

- Peter (G3PIJ)