a bit of an experiment

[jed]

Thanks for all your advice regarding transformers, Ive decided to source them from vvt, http://www.vvttransformers.co.uk/ as the are quite local. As far as I know no one has used them in an 18watt and they seem to be quite a bit cheaper than the Sowters.

Now what I was wondering was the secondary voltage straight off of the winding. Although I know its quite sketchcy but would it be feasable to run anyless than 300v maybe 265v without any Ill effects?

Would this prevent plate overload?

Jed

[RossH]

I use a Hammond 275V PT and run it through a 5AR4 and that gives me about 330V on the EL84 plates. Works excellent.

If you stick with the EZ81 it will just have lower overall voltage. Less headroom...colder bias. It will still work you may have to tweak some components to get what you want though.

~Ross

[zaphod_phil]

Now what I was wondering was the secondary voltage straight off of the winding. Although I know its quite sketchcy but would it be feasable to run anyless than 300v maybe 265v without any Ill effects?

Which transformer are you considering buying from VVT? Then we can discuss it's likely suitability. Also, Duncan's web site http://www.duncanamps.com has a free tool that lets you simulate different power supply arrangements, called PSU Designer II.

[jed]

Thanks,
I downloaded the psu designer,
3 Options......

1) 265v; VTH103300
2) 300v; VTH107300
3) Or alternatively take the cheaper option and go for tordials and run a seperate heater supply. (has anyone does this? - how does it affect tone)

Jed

[zaphod_phil]

Have you done the simulations in PSU designer? I would have thought that the 265V would be the better option. Also, are you going for a completely identical 18W clone? If not, you will save yourself some work cutting a square hole in your chassis if you don't go for the 'drop through' versions. However, you could also buy a ready-made chassis with the holes already done for you.

Regarding the toroidal transformers, John Howell in South Africa built an 18W Lite II in a 1U router box using toroidal transformers for both PT and OT, and seems very pleased with the results. There are pictures of it on the old 18 Yahoo group site, as well as on http://myweb.absa.co.za/johnhowell/1U.htm

[jed]

Thanks,
265v it is.
Im not too concerned about going totally original however I do prefer the neater drop through look, Chassis punches are no problem so it looks like thats the way Ill go. There are a few local companies (hampshire way) that'll cut the chassis holes cheaply anyway so I might not even bother doing it myself.

So phil, what do you think about a competetition to see whether anyone can build the whole amp without going to maplin or RS.

Jed

[markh]

265v it is.

I agree with Phil, FWIW.

So phil, what do you think about a competetition to see whether anyone can build the whole amp without going to maplin or RS.

You'd have to limit to UK folks - most of us have never been to either!

--mark

[Greeneyes0v0]

Only UK i know of is University of Kentucky..

Looking at the pics of Steves UK amp.. i wish we could get RS parts as easy. Alot of the marshall amps used the RS parts and Hunts caps { Radio Spares not radio Shack}
I think Jeff also went on a shopping spree over there.. Some things over here we can't get, {well in brand type.}

If there are not that many parts shops in the UK.. looks like someone would jump in and start a new business. Selling all the stuff people want or need for amps. Might be a bazillionaire.
Richie

[zaphod_phil]

That's Limey Land to you!

Unfortunately, RS no longer stock those classic transformers, nor anything much of use to tube amp builders, apart from general resistors and caps. Nearly everything they do is geared towards today's digitally-orineted electronics industry. You can get more of this kind of stuff in the good old US of A.

[zaphod_phil]

So phil, what do you think about a competetition to see whether anyone can build the whole amp without going to Maplin or RS.

You done gone crazy boy? I buy 90% of my parts from Maplin! I couldn't survive without them. Like telling someone in the US not to buy from Angela. Hardly ever buy anything from RS, though. They're web site's too cumbersome....

[jed]

Just thought it might be an intresting challenge......

Jed