Which PT for Overtone Special?

[eazilyled]

There's a pic of my build here:

http://ampgarage.com/forum/viewtopic.ph ... highlight=

[Kassie]

There's a pic of my build here:

http://ampgarage.com/forum/viewtopic.ph ... highlight=

Looks really good! very nice build.

That shiny extra steel plate is for added stability to the chassis I presume?

I measured the Ceriatone chassis holes.. they are 9.5cm by 7.6 (3.74'' by 2.99'')

The Hammond 373fx has 3.5 by 3.5

If I add washers inbetween the mounting legs, and the iron I might extend the 3.5 to just 3.74 about enough to mount at least 2 of the holes (perhaps widen the holes a bit more). The other ones I have to drill extra. I can make an extra closing plate of steel to close of the gap, and add firmness to the chassis.

[eazilyled]

Looks really good! very nice build.

That shiny extra steel plate is for added stability to the chassis I presume?

I measured the Ceriatone chassis holes.. they are 9.5cm by 7.6 (3.74'' by 2.99'')

The Hammond 373fx has 3.5 by 3.5

If I add washers inbetween the mounting legs, and the iron I might extend the 3.5 to just 3.74 about enough to mount at least 2 of the holes (perhaps widen the holes a bit more). The other ones I have to drill extra. I can make an extra closing plate of steel to close of the gap, and add firmness to the chassis.

Thanks Kassie

That steel plate came with my kit (not sure if it should have or not) and yes I believe it adds extra mechanical stability. Mercury Magnetics use them as well (see http://www.mercurymagnetics.com/pages/c ... /index.htm). I figured I may as well use it since I had it. The plate had some holes in the edges as well, and I think I used a couple of them to keep some of the wires in place.

If I remember correctly my approach was to widen each of the holes in the chassis by drilling a hole right next to each one. Then I used a file to smooth out the jagged bits to make a slot shape. Then I did same with the plate. When I mounted the PT I used big washers to add a bit of extra strength / cover up the slots.

You might be able to do use a combination of existing holes and new holes as you described. I remember considering this approach but I didn't do that with the PT for some reason and I can't remember why. Maybe it was because the new holes would be halfway overlapping the old ones and therefore tricky to drill? I was able to do that for my Hammond choke / OT though, as the chassis holes were quite different from what was required.

You'll probably figure out the best approach when you get the PT in your hands.

[martin manning]

This is a 100W? What about: http://www.hammondmfg.com/pdf/EDB290FEX.pdf

[eazilyled]

This is a 100W? What about: http://www.hammondmfg.com/pdf/EDB290FEX.pdf

I believe that must be the Twin type replacement that Kassie is considering, but it's probably worth emphasising that my PT was a Super Reverb / Tweed Bassman type replacement and would only be suitable for 50w builds.

[martin manning]

290FEX is listed as Twin Reverb, Dual Showman, Bassman 100 replacement, export primary of course. Mounting centers match, don't know about the cut-out.

[eazilyled]

Mounting centers match, don't know about the cut-out.

Good spot Martin. Kassie, I would go with Martins recommendation here especially since no chassis drilling is required.

Then there's the 291FEX which is simply described by Hammond as a '290FEX upgrade'. Mine was also an 'upgraded' version. Wonder what the difference is. Different steel presumably?

Edit: corrected model nos above to avoid confusion

[eazilyled]

Found this:

http://angela.com/hammondupgradepowertr ... 291fx.aspx

Describes the upgrade as follows:
"The 291FX is an upgrade to the 290FX featuring high grade 29M6 magnetic steel laminations for reduced losses, more surge output power, cooler operation & longer life."

[eazilyled]

Then there's the 291EX which is simply described by Hammond as a '290EX upgrade'.

To be fair, Hammonds site also describes the upgrade in more detail, I just needed to scroll to the top of the page

http://www.hammondmfg.com/guitarLinePWR.htm

[martin manning]

Yes, there is 291FEX (240V primary) too. Here's Hammond's listings: http://www.hammondmfg.com/guitarLinePWR.htm

[Kassie]

290FEX is listed as Twin Reverb, Dual Showman, Bassman 100 replacement, export primary of course. Mounting centers match, don't know about the cut-out.

Ok... I did the following calculation.

B+ (4x 6l6 + 3x 12ax7 = 4x 54ma + 3x 1.2ma = 219.6ma) Twin has 500ma

Heaters (4x 6l6 + 3x 12ax7 = 4x 900ma + 3x 300ma = 4.5a. Twin has 5.5a

However, I will need an extra filament transformer for the relay.

[martin manning]

There is probably enough conservatism in Hammond's filament rating to run EL34's if you want. A small extra transformer for the relays is no big deal... Get one from Radio Shack like DUmble did.

[Kassie]

EasilyLed

This is the PT you have been using for 50 watt.

http://www.hammondmfg.com/pdf/EDB291EEX.pdf

it has 276ma on the secondaries. If my calculations are allright, that the tubes use 219.6ma... then it would be okay to use that one as well.. or am I missing something here?

[Kassie]

There is probably enough conservatism in Hammond's filament rating to run EL34's if you want. A small extra transformer for the relays is no big deal... Get one from Radio Shack like DUmble did.

I live in the Netherlands.. prefer Europe shops for shipping/insurance costs... so right now I am going to look for a hammond 6.3v transformer.

[Kassie]

Found a couple of models. http://www.hammondmfg.com/266.htm

Edit: The 266F6 model looks allright... 6.3v at 0.3a... I may want to include a cornish buffer circuit to the fx loop. So 0.3a would be enough for that? Or do I want something slightly higher in amperage?