6G2 Power Transformer Spec

[electrical]

I have started acquiring the parts including a chassis for a 6G2 from Mojotone. Mojotone no longer sells the MOJO756EXLV power transformer which the chassis is cut out for; based on the mounting spec of the MOJO756 it seems the chassis is cut for a Deluxe power transformer. I've contacted Heyboer and they're willing to reproduce the 756LV as a custom wind for a modest uncharge; I have all the tubes I need on hand already, so I'm willing to spend a few extra dollars to get the spec of the power transformer correct. Heyboer's spec for the 756LV secondary is 330-0-330 at 60ma. Given the B+ of the 6G2 is 315Vdc that secondary seems a bit high, though I am not sure how much voltage is dropped by the 5y3. Heyboer is willing to modify the secondary taps and current rating for the same price as the 756LV as this is already a custom job.

What is the appropriate spec for the 6G2 secondary tap (and for that matter, what's the correct way to spec power transformer secondaries - both voltage and current - for guitar amps)? How do I figure out how much voltage is dropped by the rectifier, and how does this change for tube or solid state? I was once told by a friend in radio that when going from primary ac to rectified dc voltage that a good general rule is to multiply by 1.2 for tube rectifiers (and I believe he said 1.4 for solid state though I can't quite remember), is this general rule correct?

For this amp I want to optimize the overdriven tone, and I'd prefer a sweeter and more compressed overdrive tone and lower overall volume rather than clean headroom. Would 265-0-265 at 100 ma get me there?

6G2 schematic attached for reference.

[bmccowan]

Just one point of reference. I built a 6G2 and used a ClassicTone 18027 PT. Sadly no longer available, but some say Heyboer bought their tooling and such. Anyways the PT offered two sets of secondaries. I used the 275-0-275 100ma set as I had similar goals to yours. The amp is great IMO - B+ voltage result was right on spec.
Hardest part with this amp is dialing in the sweet spot for the trem.
BTW, Heyboer has a great website (sarcasm) You can even download a spec spreadsheet that has this info: "this is an empty spreadsheet"
Still, they make good stuff. You might also check out Hammond and Musical Power Supply.

[Latole]

Hammond ;

https://www.hammfg.com/fr/electronics/transformers/classic/290?referer=787

[Esquirefreak]

I used the Hammond 290CAX for my 6G2 and used the 275V HV taps. With a 5Y3 and the amp biased at ~60% I had 300V on the plates.

/Max

[electrical]

I had looked at the Hammonds (specifically the 290AX), however they are not the correct size for the Mojotone 6G2 mounting holes, and I would rather have an electrical than mechanical solution to this amp as I’m more electrically inclined.

Thanks for the help, I have a Heyboer on order at 275-0-275 with 100ma, 2A each on the 5 and 6.3 volt taps.

[dogburn]

Glad you got that worked out. I built a 6G2 using an old standup power transformer from a Voice of Music phono amplifier, and it sounds great. I bought the VoM amp off ebay on a whim, and got some useful tubes and the PT - and looking at the specs I saw it was most suitable for a 6G2, so that became my first project. So basically took the opposite approach of getting a transformer and figuring out what amp to build.