Converting a 10 watt to an 18 watt?

wilko · Post by **wilko** » Fri 07/11/03 7:46 pm

I know this may seem like sacrilidge to some, but I may want to do this. How would I go about it? is there an easy site, or thread that I've missed?
Is it a doable poroject?

we're talking 1930 poular combo, into a 1958 18watter spec. I've read that it's supposed to be a possibility...

thanks in advance...

loverocker · Post by **loverocker** » Sat 07/12/03 5:31 am

Pretty sure that you'd have to change the whole thing - PT (too little juice available, no rectifier heater feed?), OT (presumably smaller?) and circuit. In which case, I reckon it'd be better all round to order up a complete new chassis that you can just swap into place of the 10Wer's. Wouldn't cost much more and you'd still have a 100% unharmed 10Wer for future sale to fussy collectors.

Just my 2p's worth.

Post by **zaphod_phil** » Sat 07/12/03 9:02 am

I am told that the 10watter uses exactly the same chassis as the 18watter, and you can see the holes in it for the other tubes that aren't there. I wouldn't be surprised if for cost reasons it doesn't have the same Xformers as well. However, these amps are very rare and worth huge amounts of money. To start modding them would be to destroy their market value. So Loverockers suggestion is a much sounder one. Build a complete 18W chassis and use it to replace the 10watter one.

PS: I'm not sure what Loverockers reference to a rectified heater feed was supposed to mean, as neither the 1930 nor the 1958 use a DC heaters supply.

loverocker · Post by **loverocker** » Sat 07/12/03 10:39 am

zaphod_phil wrote:PS: I'm not sure what Loverockers reference to a rectified heater feed was supposed to mean, as neither the 1930 nor the 1958 use a DC heaters supply.

Oi, I know that! You turned my 'r' into a 'd'.

I am refering to the rectifier's heater supply. Wilko - if you can post pix of the power transformer's wires, it'd only take a second to check to see if your 10Wer has a second (but unused) heater supply for the non-existent EZ81.

If Phil's right and Marshall did use the same transformers, it'd be an easy conversion with its existing hardware.

wilko · Post by **wilko** » Sat 07/12/03 10:52 am

The 10 watter is in the mail. I should have it by this Friday.
I know I'll be looking at the transformer to see if I can tap it to run on 110-120v. Other than that it's a step up for me.

Post by **zaphod_phil** » Sat 07/12/03 2:10 pm

loverocker wrote:
zaphod_phil wrote: Oi, I know that! You turned my 'r' into a 'd'. I am refering to the rectifier's heater supply. Wilko - if you can post pix of the power transformer's wires, it'd only take a second to check to see if your 10Wer has a second (but unused) heater supply for the non-existent EZ81. If Phil's right and Marshall did use the same transformers, it'd be an easy conversion with its existing hardware.

My eyes are playing tricks with me! I was really scratching my head about something you never wrote.

OK, the next issue is that the 1930'sdesign is very different from the 18Ws' -it's far more than just using ECL86s for the power stage and PI. You would have to basically gut and rebuild the whole thing from scratch. Hence I again recommend the idea of building a saparate 18W chassis, which will fit into the same cab instead of the 10watter.

Post by **zaphod_phil** » Sun 07/13/03 3:32 pm

Well, Loverocker posted thei eBay auction link in the 'By the BBQ' section and it has soem excellent 1930 10watter chassis pics. http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 2544012995

The 'Supersize' pictures are very good quality and show a lot of detail. You can see the PT and its connections, and you can also just about see the holes for the tubes that would be used for an 18W, which have been covered by bolted-on blanking plates.

loverocker · Post by **loverocker** » Mon 07/14/03 3:27 am

You've got a better memory than me, Phil

I'd forgotten about that.

The PT pic is a bit dark but it seems to have only two outputs: the HT supply with CT on the left, and the 6.3V supply with CT on the right?

Post by **zaphod_phil** » Mon 07/14/03 10:18 am

I thought I saw what looked like a couple or so unused lugs on that Xformer. It might be a good idea to save the jpeg and ligten it up in a graphics package...

wilko · Post by **wilko** » Mon 07/14/03 10:25 am

The seller of that chassis had tyhis to say:
All the small Marshall combos are wired for 220-250 volts. A step-up transformer is needed for these. All 10 18 20 watt combo's are like this. You can have 110-120 volt transformer put in there. They never came with a 120 volt tap, only the 20 watt heads came with a 120 volt tap and they were far and few.

loverocker · Post by **loverocker** » Mon 07/14/03 10:45 am

Phil, in fact I did the brightness/contrast thing

Take another look. The unused lugs appear to be at the top (i.e. AC mains supply side). From the (few) UK amps I've looked at these tend to be 200V/230V/250V primary feeds (designed for different European countries perhaps?). As Wilko's seller said - 110V/120V don't show up on these old amps.

There are then six lugs along the bottom, which appear to be three lugs for HT+CT and then three lugs for 6.3V+CT.

Hey, Wilko, let us know when it arrives - this is bound to be a FAQ in years to come so a definitive and hands-on answer'd make the archive more useful.

wilko · Post by **wilko** » Mon 07/14/03 10:50 am

I'll let you know what I find out. I've got an external transformer on order, and this chassis looked like a good candidate to build an 18 or 20 as a swap-out chassis for the 10 watter on the way. That way I'd still have the original amp, plus the higher powered option.

Wannatone · Post by **Wannatone** » Mon 07/14/03 4:30 pm

Wilko,

Congrats on the 1930!

I would save the original chassis, too. There are very nice chassis/tranny or complete kits available.

Hope you get the amp soon, and... remember to post some pics

wilko · Post by **wilko** » Wed 07/23/03 1:01 pm

The amp arrived today. I'm at work, so I can't dig into it yet.

Here's something interesting: on the plastic plate on the back it lists the voltage as 110/230 volts at 40/60 cycles.

loverocker · Post by **loverocker** » Thu 07/24/03 3:00 am

Hmmm.... that'd be useful.

Let us know what it's like cranked. I've never heard an ECL86-powered amp.

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Converting a 10 watt to an 18 watt?

Converting a 10 watt to an 18 watt?