Transformer Conundrum: 1965 Gibson GA15-RVT

[widget2640]

Hey guys - thanks in advance for any insight.

So I'm a bit out of my depth - having brought my GA amp to a tech in town (actually the second tech to take a stab at this beast!) Things appeared to be moving along - he replaced the caps, blown fuse, swapped out the old two prong plug etc...The tech identified the culprit preventing the amp from working as the power transformer (T1). The original was toast - so he had me purchase this one: https://www.mojotone.com/amp-parts/P...er-Transformer

This is where he got flummoxed - it was clear after several weeks that the transformer we got from Mojotone was not going to work - simply couldn’t figure out how to mount the thing. . This is what the tech said "the transformer we got from Mojotone is a muti-tap transformer and isn't specific to the amp (Mojo does say on their website that it'll work for Gibson GA type amps - but alas it appears not mine). It has 2 more legs on the secondary side than what the original transformer had. I need to match up voltages from the transformer to the amplifier. This needs to be correct or damage to other components will happen - if it works at all..."

He's suggesting that this replacement would work for my amp: http://bit.ly/tubedepottransformer

I've also attached a photo of the original transformer as well.

Any help or insight would be much appreciated.

I've perused several posts on here where the following transformers were suggested.

MERCURY

https://www.mercurymagnetics.com/?s=...t_type=product

HAMMOND

https://www.hammfg.com/electronics/t...rs/classic/200

!. Which would be the optimal, best Transformer to use on my amp?

2. Any other insight as to mods or upgrades that may also either mitigate future issues or improve to overall tone of the amp?

Much thanks again for any help you can provide.

MJL

[Jazz P Bass]

Whoa!
This is the schematic for the GA15RVT.
GA-15-rvt-1965.pdf

The power transformer that you purchased will Not, as your tech ascertained, work.
That one is clearly marked as for the RV series of Gibson amps.

Your tech may have gotten confused as the link you posted as his replacement is for the Output Transformer.

The Mercury transformer that you linked is a Reverb Driver Transformer.

The Hammond 272FX should work.
Hammond EDB272FX.pdf
It may take some work to get it to fit in though.
The 5V winding can be shrink wrapped & tied off as the RVT does not use a tube rectifier.

Also, the Edcor has been suggested here: https://music-electronics-forum.com/...ad.php?t=29735

[Chuck H]

I don't think the Hammond 272fX is suitable either. At 600VCT into a diode rectifier it's going to result in much higher B+ voltage. It's also a lot bigger and mounts on a different plane than the original unit which could cause insurmountable mounting problems. I think a more suitable transformer might be:

https://www.hammfg.com/files/parts/pdf/270DAZ.pdf

It'll still be larger and produce higher than stock voltage, but not as much as the 272FX. It's the smallest "Z" mount offered in the line. It probably has a closer current spec too.

[Chuck H]

Consider that you bought the first unsuitable transformer on this techs suggestion. And consider that the next one suggested is also unsuitable, being the wrong type of transformer. And the third one isn't even in the ballpark.

I might start to question if this tech is even on the right path. Even if he/she is, are they capable of a retrofit installation? I'm confused about how all the other work was scheduled when the amp doesn't even power up in the first place, as a bad power transformer would suggest. I don't think I would continue with this tech, but I don't know the whole story.

[widget2640]

Thanks for responding JPB

He very well may have sent the wrong link - who knows at this point. As for the Mercury - I mistakenly scooped that off another post thread regarding a similar amp as mine.

Aside from the EDCOR and perhaps the Hammond - which seem to require some level retrofitting and may still not be ideal.

If it was your amp what transformer would you use? I'm just trying to get the best info for him I can at this stage.

Thanks again

MJL

[nosaj]

Thanks for responding JPB

He very well may have sent the wrong link - who knows at this point. As for the Mercury - I mistakenly scooped that off another post thread regarding a similar amp as mine.

Aside from the EDCOR and perhaps the Hammond - which seem to require some level retrofitting and may still not be ideal.

If it was your amp what transformer would you use? I'm just trying to get the best info for him I can at this stage.

Thanks again

MJL

Considering Chucks comments , we're not even sure the PT is bad or if your tech ruined it, etc. Time to find someone else. A tech would not have the customer hunting for a part , a good tech for the most part be able to source most things.

Looks like heyboyer rewound one last yearhttps://music-electronics-forum.com/...ad.php?t=29735
nosaj

[nosaj]

Considering Chucks comments , we're not even sure the PT is bad or if your tech ruined it, etc. Time to find someone else. A tech would not have the customer hunting for a part , a good tech for the most part be able to source most things.

Looks like heyboyer rewound one last yearhttps://music-electronics-forum.com/...ad.php?t=29735
nosaj

Check with some of these stores and see who they recommend in the Portand, Maine area
nosaj
https://www.yelp.com/search?find_des...Portland%2C+ME

[Chuck H]

.., we're not even sure the PT is bad or if your tech ruined it, etc. Time to find someone else. A tech would not have the customer hunting for a part ,..

That^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The first part purchased on the techs advice was wrong. And I'll guess at least difficult, if not impossible to return for any monetary recovery. If the links sent were incorrect that's just another ding. If they weren't incorrect then they were wrong, again. And then there's the point about other work performed.?. If an amp doesn't power up (or have filament voltage or whatever) then that is the priority. I immediately wondered if the "tech" didn't work on the power supply, make a mistake and burn up the PT upon powering up. Clearly this person doesn't know what transformer to put into the amp based on their first recommendation and/or is too unfocused to have noticed it was wrong on that or this next time and/or even to send the correct links. Too many mistakes to write off for me.

[Chuck H]

Ok... I just went to the Mercury link above, AND... The reverb transformer that appears in your face is a "featured" product. The link is for a search at the site with keyword GA15 rvt. The first list transformer is the GIB-GA17-P, which looks like it may be correct when checking the specs for the Gibson GA17 RVT. A lower wattage amp, but then the power transformer in the pic above is a bit small, so.?. Anyway, it could be the correct link and the correct transformer and I might be bashing this tech prematurely. But I WILL give him a ding for choosing Mercury iron at some two or three times the cost of other options

EDIT: I see now that the Mercury transformer was a suggestion from THIS site (bow's head in shame). And that the "tech"s link is, indeed, for an output transformer and not a power transformer. So they're back on the gooble gobble list.

[Bloomfield]

I had a hard time reading that schematic, but maybe this Hammond 290XX or another Blues Jr. replacement might do the trick. The stated voltage is after rectification so seems reasonable. I'm not sure if the Gibson transformer is horizontal or vertical mount; the Blues Jr. is horizontal.

http://www.nextgenguitars.ca/product...ansformer.html

[Leo_Gnardo]

Check with some of these stores and see who they recommend in the Portand, Maine area
nosaj

Hoffman also has a list of recommended techs: https://el34world.com/service.htm

Don't neglect the not too far away New Hampshire zone.

[widget2640]

Consider that you bought the first unsuitable transformer on this techs suggestion. And consider that the next one suggested is also unsuitable, being the wrong type of transformer. And the third one isn't even in the ballpark.

I might start to question if this tech is even on the right path. Even if he/she is, are they capable of a retrofit installation? I'm confused about how all the other work was scheduled when the amp doesn't even power up in the first place, as a bad power transformer would suggest. I don't think I would continue with this tech, but I don't know the whole story.

Thanks again for responding Chuck - While I am not filled with confidence this guy can ultimately get my amp fixed - some of the "suggested fixes" are my fault just trying to find info and some is the veritable rats nest of wiring (and less than comprehensive schematic) and a shit ton of conflicting info out there. I guess I'd ask if it was your amp what transformer do you think would be the optimal choice? EDCOR? Any other mods or upgrades you may have done, or heard of or might suggest?

Thanks

[Chuck H]

I had a hard time reading that schematic, but maybe this Hammond 290XX or another Blues Jr. replacement might do the trick. The stated voltage is after rectification so seems reasonable. I'm not sure if the Gibson transformer is horizontal or vertical mount; the Blues Jr. is horizontal.

http://www.nextgenguitars.ca/product...ansformer.html

The Gibson in question has a laydown PT mount. Unfortunately it requires a CT HV secondary and that 290XX doesn't have one. Changing rectifier type is no great shakes IMHO. The 290XX is also somewhat larger, so it would require some retrofitting, if it fits at all. Vp would be about 30V higher than stock I guess. Certainly no worse than my suggestion above.

[drewl]

How about a Deluxe Reverb PT?
If the trans is bad.

They're about the same and cheap.

[Chuck H]

How about a Deluxe Reverb PT?
If the trans is bad.

They're about the same and cheap.

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The amp in question has 300Vp using a diode rectifier. A Deluxe Reverb PT would push it to about 460Vp It's also a laydown type mount rather than upright.