When was Radiospares' Deluxe Output Transformer first added to RS catalogue?

[Valvepower]

Hello,

I’m trying to ascertain roughly when Radiospares included the Deluxe output transformer in the catalogue – I suppose I’m just curious.

The first mention I can find of the Deluxe output transformer was in the Practical Wireless guitar amplifier in the May 1964 edition, so using that as a starting point, it would have been in the 1964 catalogue, but when did it first appear in the catalogue – if it did appear in earlier years.

I’d date the transformer I have here to the early 60s and is fitted to a home brew amplifier, which deserves to be running again.

Regards
Terry.

[toprepairman]

Hi Terry.
Sorry can't tell you when first appeared in the RS cat.
As you know these were built by RF Gilson. with the style of construction known as SIM.
Their WO1546B was made for the Mullard 20 Watt amplifier.
7000 Ohms 20% taps and 20 Watts undistorted from 30Hz to 15K.
Flat 10Hz to 40 k at one Watt. Grain orientated Lams.
The same size and style also used for the Pye 5/8, though I don't know if that also had grain orientated or plain steel as it would seem a bit overkill for just 8 Watts.
The 20 Watt version being famously used in the Marshall JTM45 guitar amp though it seems an awful waste of a superb transformer in a guitar amp.
The price as quoted in the 1962 price list was 92/6d. the price list was issued in 1960 so they certainly were available then or earlier.
Regards
Henry

[toprepairman]

Hang on a minute, could be jumping the gun here.
Was the RS version the one that had three sets of primary inputs, giving slightly differing input z's?
It's the same SIM style and size, but that one does not appear in the 1960 issued '62 price list.

[toprepairman]

Interesting in how on that style the laminations were interleaved in bunches rather than individually, I wonder why they did that?

[Boulevardier]

Originally Posted by toprepairman

Hang on a minute, could be jumping the gun here.
Was the RS version the one that had three sets of primary inputs, giving slightly differing input z's?
It's the same SIM style and size, but that one does not appear in the 1960 issued '62 price list.

I have one of these RS transformers somewhere in the shed. I bought it second-hand in 1964-65 as part of a scrap chassis, so it must have been late '50s/early '60s. I can't get at it immediately to check if there's an RS part no. (it's raining, hailing and snowing cats-and-dogs at the moment).

It has ultra-linear taps on the primary, and I later used it successfully in a Mullard 5-10 build.

Have you seen this?
https://www.vintage-radio.net/forum/...7&d=1145649242

Mike

[kalee20]

Originally Posted by toprepairman

Interesting in how on that style the laminations were interleaved in bunches rather than individually, I wonder why they did that?

It'll give a slightly softer saturation characteristic.

Fully interleaved, the inductance of the transformer will be (almost) as much as the iron will be capable of. But it won't be able to withstand more than a few mA of unbalanced DC between the standing currents of the two valves it's connected to, without saturating and losing a lot of its inductance.

With the laminations butted rather than interleaved, there'll be the equivalent of a very small air gap, which will reduce inductance considerably. But any standing unbalance in current will reduce the magnetic field in the core by the same proportion, so the transformer would be able to cope with a much greater unbalance without heading into core saturation. (Deliberately adding a non-magnetic shim can allow the transformer to operate with tens of milliamps of standing DC, at the expense of a further drop in inductance, which is what is done in single-ended transformers of course).

If the laminations are interleaved in bunches, the inductance won't be as high as fully interleaved, but it will still be pretty high. If there's just a bit of standing DC, the iron adjacent to the interleave interface will tend to saturate, but towards the centre of the bunch won't. So you get a slight drop in inductance. More unbalance and the saturation penetrates further towards the centre of the bunch. So inductance falls a bit more. You can see you get a soft, smooth reduction in inductance with increase in DC bias.

So, the transformer will be more tolerant towards mismatching of valves. It's not particularly precise, but it does have merit. For the complete amplifier, it's never going to be as good as a fully interleaved transformer working with accurately matched valves, but it does mean you can plug-and-play much more easily.

[toprepairman]

Very interesting, makes perfect sense, thanks for that.

[Ed_Dinning]

Hi Peter thanks for the explanation on the stacking of lams om OPT's, but does it have a similar effect om mains transformers, or is it simply a production technique to save time?

Cheers, Ed

[kalee20]

I've not seen it done on mains transformers Ed - if so, I'd say it is just a time-saving exercise (of dubious value as the lams would have to be counted each bunch).

I do have a Trix amplifier with O/P transformer laminated in bunches (it's 2 x EL84 with common cathode resistor, so not good for balance with unmatched valves), and the mains transformer laminated individually.

[Valvepower]

Hello,

Just picking up on this thread as I popped up to Harwich for a couple of days to go along to the Radio Caroline event held in Harwich on Thursday, anyway back to the job in hand…

Thanks for all the replies.

Going by the posts, I’m thinking the transformer in question first appeared in the early 60s – possibly around 1963.

Being honest, I hadn’t really thought about the laminations being interleaved in bunches – I’d seen it, but it just didn’t register as to its effects. It does make me think this may been an unintentional attribute which might explain its popularity in guitar amplifiers? I figure when Marshall et al, first used it, it was because it was readily available, and the laminations may have caused something unintentional.

This home brew amplifier restoration project has taken a slightly different path… I’m going to lower the HT by 30% using a mains transformer with a lower HT winding and replace the De-Luxe output transformer with the lower power Radiospares Heavy Duty transformer. I’m going to liberate the Radiospares De-Luxe output transformer and use this in a JTM45 build as I have a suitable mains transformer and few other bits in the workshop.

Anyway, I’m now on the lookout for very early 60s Radiospares catalouges

Terry.

[toprepairman]

Seems a bit of a waste to me. The 'Heavy duty' isn't great for HiFi but would make a perfect guitar amp and the 'De-luxe' is perfect for HiFi, and much too good for guitar.

[radiomobile]

The "Heavy duty" is rated 15 watts and the "Deluxe" 30 Watts so no comparison really.

[Valvepower]

In all honesty, I really was in two minds what to do with the output transformers as I really didn’t want to just harvest the De-Luxe output transformer and discard the home brew amplifier because it really, really doesn’t deserve that fate.

It was decided when I encountered problems with the basic design of the home brew amp, which is causing some problems, so I decided to reduce the HT and thus the power and use the heavy Duty output transformer.

I don’t want to get tied up with guitar amplifier construction, but the De-Luxe could be better served used in a guitar amplifier as these amplifiers appeal to the young guitarists thus giving another life to these parts for years to come

Terry.

[toprepairman]

Indeed, something of a quandary.
I also do have a single De-luxe, so one solution could be to let me have it to build a nice stereo amp (he says with tongue in cheek and little hope of success, Lol).

[Valvepower]

Hello,

Quick question… has anyone rewound or stripped down a Radiospares De-Luxe output transformer and got the construction of the layers etc., in the primary and secondary.

Maybe there is an opening for an output transformer dating agency Lonely Radiospares De-Luxe output transformer seeks long term partner to enter into a stereo amplifier relationship project … Must have HILL (High Inductance and Low Leakage)

I have both a Gilson WO892 and WO710 looking for a partner…

Best keep on topic though…

Terry

[toprepairman]

I also have a spare 710 looking for a friend.

[toprepairman]

Swap my 710 for your 892?

[Valvepower]

Henry,

I’ve been mulling this over since yesterday when you said you have WO710 looking for a mate

We could partner up the two WO710, but I want to keep the WO892 even if I can’t find a partner this is because it has 3, 7.5 and 15-Ohm taps making it more useful with more modern speakers.

Terry.

[toprepairman]

Ok Terry, that's fine.
I do have one amp that already has a 892 so would have been nice to build something to partner it but do completely understand your preference to keep it, (I would).
Henry