Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: DummyLoad on October 06, 2015, 10:39:25 pm
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scored these two off craigslist earlier today for $650.00 for the pair. a friend wanted the reverbrocket2 when i told him it was a 1965 model.
https://www.dropbox.com/s/m01x5lpaw67oh96/20151006_194227.jpg?dl=0 (https://www.dropbox.com/s/m01x5lpaw67oh96/20151006_194227.jpg?dl=0)
we have a reverbrocket2 that's kind of rough on the outside, but is/was pristine inside and untouched. the second amp is a gemeni I in similar condition. both amps work, however, the reverbrocket2's speaker surround is shot. it's a jensen concert C12R. all the dates confirmed it as being a 1965 model and the iron is all original.
both amps have the original ampeg brand 7591 and the reverbrocket2 has a bugle-boy 12AX7, however, the 7199 looks like a late 70's sylvania. the 7591's are made by sylvania. i'm working on the reverbrocket2 now, and will have it done shortly minus a 22uF 450V F&T. both are getting 3 wire power cords, new power supply caps, output stage bypass caps, and new/re-coned speakers. i put a jensen P12Q in the reverbrocket2 until the C12R is returned.
these (http://freemantuell.com/=) guys do a bang up job with vintage speaker re-coning and the C12R is headed there tomorrow.
some amp porn.. a few peeks under her skirt.
https://www.dropbox.com/sh/n0mc7trdustqo7a/AAA3Ei6llWQr_8nUyG1HdsjMa?dl=0 (https://www.dropbox.com/sh/n0mc7trdustqo7a/AAA3Ei6llWQr_8nUyG1HdsjMa?dl=0)
--pete
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Lovely score.
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Wow those guts are nice and clean! Great find!
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Those Reverbrocket's are GREAT sounding amps. Very nice score!
Jim
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thanks guys!
the reverbrocket2 is finished! well, almost. minus the pilot light and the handle, which are on the way from fliptops. sounds really nice; the reverb is not as thick as i thought it would be, but the trem sounds really good. overall i'm very pleased.
i used a 40-20-20-20 J&J for the main filter, 2 22uF F&T for the preamp filter and moved the output stage bypass to the board. schematic called for a 20uF 25V i stuffed a 47uF 50V in there as that's all i had close to 25V needed. i had to drill two new mounting holes for the J&J filter.
the original filter was 60-40-10-20. the 25uF section was 25V for output stage bypass and the 40uF and 10uF were strapped together for screens and preamp. i strapped 40+20 to OT CT and 20+20 for the screens. i added 3 wire grounded power cord. it's dead quiet and the foot-switch works well. the tremelo knob is washed out, the new owner will replace it when he has the scratch.
i'll post pics of the work after i install the pilot lamp and handle next week. there is a copy of the schematic on the rear panel. it's flaking away so i took a high-res photo of it if someone should want a schematic to a GS-12-A.
--pete
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schematic.
https://www.dropbox.com/s/l34ybjx2wzuae5f/20151007_003824.jpg?dl=0 (https://www.dropbox.com/s/l34ybjx2wzuae5f/20151007_003824.jpg?dl=0)
--pete
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Really nice scores!
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I always thought the old blue diamond amps were the coolest looking amps. My first real amp was a Gemini II. Hope you get the Gemini I going.
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Just a quick rookie question....nice hi-rez schematic pic btw
What is/was the design goal/benefit of having the screen supply (B) branch off of the 1st node (A) instead of being in series with the rest of the B+ line?
Less voltage drop downstream obviously, but is that it?
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I always thought the old blue diamond amps were the coolest looking amps. My first real amp was a Gemini II. Hope you get the Gemini I going.
the gemini I works. yay! no abnormal or excessive hum, but it's in rough shape and the front panel is nearly unreadable from corrosion. it needs a 3 wire power cord and some new knobs at the very least. reverb and trem both work and it looks like it has the original power tubes. it's going up on the bench tomorrow for the power cord, and probably new power supply caps. foot-switch works too. i need to check out the speaker too as it sounds like the surround has tearing. i'll probably just slap in a weber or jensen alnico and flip it on fleabay.
--pete
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these are both done. the reverbrocket2 has a weber ferromax speaker and the gemini I has an eminence black mountain.
to the gemini I i added a 3 wire power cord, 3 mullard 12AX7 and buttoned it up. all the caps are still good and hold charge. i ordered new caps and they are on the way, but probably won't get around to installing them until the holidays. replaced the knobs with black chikkin haids until the replacements arrive.
these knobs (https://www.alliedelec.com/davies-molding-1550ag/70097812/) are as close as i can find to the originals. they look a lot like the 5$ part fliptops is selling.
very happy with the gemini I for now. reverbrocket2 owner picking up his tomorrow.
--pete
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Just a quick rookie question....nice hi-rez schematic pic btw
What is/was the design goal/benefit of having the screen supply (B) branch off of the 1st node (A) instead of being in series with the rest of the B+ line?
Less voltage drop downstream obviously, but is that it?
yes, that's it. keeps B+ up for pre-amp stages. gain structure design inclusive and as a result, both of these amps have superb headroom for 20W. this is my first experience with ampeg combo amps.
--pete
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Great score! Thanks for all of the gut shots and especially the schematic. I wasn't able to find that exact circuit in the Library here. Hoping I can see it well enough to figure it out - or at least attempt it.
Cheers,
Chip
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Great score! Thanks for all of the gut shots and especially the schematic. I wasn't able to find that exact circuit in the Library here. Hoping I can see it well enough to figure it out - or at least attempt it.
Cheers,
Chip
there were two - i deleted the picture that was blurry on the input circuits. link below is the best shot of the schematic.
https://www.dropbox.com/s/9jxsy5eek10jyed/20151007_190258.jpg?dl=0 (https://www.dropbox.com/s/9jxsy5eek10jyed/20151007_190258.jpg?dl=0)
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there were two - i deleted the picture that was blurry on the input circuits. link below is the best shot of the schematic.
https://www.dropbox.com/s/9jxsy5eek10jyed/20151007_190258.jpg?dl=0 (https://www.dropbox.com/s/9jxsy5eek10jyed/20151007_190258.jpg?dl=0)
Thanks Pete!
I was trying to read the darned thing on an iPad. Big computer screen works much mo' better! I was thrown off by the tube chart being in reverse of how the tubes appear on the schematic - DOAH!
THIS appears to be the correct schematic, no? (http://el34world.com/charts/Schematics/files/ampeg/Ampeg_gs-12-r.gif)
Couple of minor differences I saw:
He shows a 100uf bypass cap on the second 12AX7 cathode where yours has none.
Cathode bypass cap on 6U10 reverb recovery stage .5uf in yours, .1uf in Piazza's, plus he shows a 390pf treble bleeder from plate to cathode your amp doesn't have.
Tremolo wobbler cathode resistor 4.7K in yours vs. 3.3K
The network around what I ass-u-me is an optocoupler for the tremolo looks slightly different.
20uf vs. 25uf cathode bypass cap for power tubes shouldn't make any difference.
I like the cyclops P.L. smilie symbol by the way (pilot light).
I really appreciate you sharing the clearer schematic. Had no idea how much variation there was in "Reverb Rocket" circuits! Holy smokes, there's an R-12-R version in the library with 6V6 power tubes, bias vary tremolo, and a paraphase inverter (instead of the cathodyne seen in most of these including yours).
Speaking of tremolo, I'd never seen it inserted right after the first triode and before the oddest TMB tone stack ever.
Then again, Fender "Deluxe" covers a heck of a lot of ground from the Deluxe model 26 to the "Deluxe 90" (wish I'd never seen that dog's breakfast of a schematic).
It actually was the phase inverter I was most interested in until I realized that a 7199 is just a wee bit different from a 12A_7. Apparently Ampeg used DC coupled cathodynes, AC coupled with DC bias, and paraphase, all in different Reverb Rocket amps.
The transformer-less reverb also intrigues me. From various YouTube clips, it sounds pretty darn lush on some of these amps.
Thanks again,
Chip
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>THIS appears to be the correct schematic, no?
yes, i believe that is it.
>The network around what I ass-u-me is an optocoupler for the tremolo looks slightly different.
wonder which is right? the high res pics should reveal that.
> 20uf vs. 25uf cathode bypass cap for power tubes shouldn't make any difference.
no, i stuck a 47uF in this amp. no noticeable change in tone from before the service.
they are unique amps. very cool sounding unique ones at that.
in other news, it seems like my gemini may have lunched the tremelo optocoupler. :sad:
--pete
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Pete -
If you look at the optocoupler in Oliver's G-300, it appears to be like yours. Unfortunately, I don't have any info on the one in mine, as he built it using a pistol shell casing. The light-sensitive resistor is glued into the primer hole, and another hole is drilled across the casing with the lamp inserted all the way through and glued. The end of the casing is crimped. There was a piece of electrical tape wrapped around the casing, but one end was melted exposing the bulb. It works just fine without the tape. I love homemade stuff.
Jack
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jack, thank you for the information. i have a replacement on the way from fliptops.
--pete
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i have a replacement on the way from fliptops.
Can you post a link to your replacement? I've made a number of purchases from him, but that's one item that I haven't given a look.
I made my layout drawing, because I will need to replace the board in mine. I don't know if I will need another optocoupler, but just in case, I'll document your replacement.
Jack
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jack, link below to ampeg optocoupler.
http://www.fliptops.net/catalog/p-100087/tm1m1-r-tremolo-module-for-vintage-ampegs (http://www.fliptops.net/catalog/p-100087/tm1m1-r-tremolo-module-for-vintage-ampegs)
--pete
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Thanks a bunch. Got it saved.
Jack