I had the good(mis)-fortune to purchase, on eBay for what I think is a very reasonable price, a full set of iron for a Gibson GA15-RVT. This includes the PT, OT, RT, and interstage tx. Naturally, this is conspiring to butt in front of my idea to build a low power, all octal, but I diverge and I've got a bunch of questions that I could use some groupthink on.
My intitial thought was to build the GA15-RVT circuit. However, I need the interstage tx for my GA20-RVT. The Hammond replacement sounds like [pick your favorite nasty word here]. Considering that MM charges $60 plus s/h, this alone made the purchase a good one, but again, I diverge. I'm thinking that I can build a cathodyne PI off the driver tube One problem is that half this dual triode runs the tremolo, so I'm going to need either a 12AX7 or 6EU7 for that. But for the PI, I'm not clear about the best pick. If I don't want to add a tube, the logical option seems to be to build it with a 12AX7/6EU7 or use a 12DW7, with the "12AU7" half for the PI. I'm not clear about the issues and how to get to a decision about this.
The next consideration is the reverb. This would be my first reverb build. I am assuming the tank is the same as the GA20-RVT, which is a 2 spring Gibbs, that meters 177z input and 181z ouput. In both cases, the RCA jack sleeve is grounded to the chassis. The numbers on the tank 1122 and 6607 don't seem to mean anything. Twisted pair on the input jack and coax on the output jack. The schematic shows one leg of the output grounded. The tank most closely resembles the Accutronics Type 4, but none of what's listed on the website matches this tank. Suggestions on a tank would be very helpful.
The first dropping resistor in the B+ supply ladder (between the 1st and 2nd filter caps) is shown as 270z. The GA20-RVT (similar in many respects) has a choke. 270 seems rather, well, wimpy. Comments on what you might do?
Thanks.
Phil
Oh, schematic is here: http://www.schematicheaven.com/gibsonamps/ga15rvt.pdf
Gibson GA15-RVT
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Re: Gibson GA15-RVT
I'm not much help Phil because I've not done a whole lot to my GA-19RVT yet other than get it basically working. I wrote Accutronics asking for a tank recomendation and didn't even receive the courtesy of a reply. Mine doesn't have a tank. Dartanion has a GA-19RVT in minty condition that I haven't had the time to take a look at yet but somewhere on the forum here in my thread about my amp somebody made an accutronics tank recommendation based on the experience of somebody trustworthy. For what it's worth, the concertina is a zero gain PI so your thinking is probably pretty good there.
Keep us posted. Use 12AX7s and leave the 6EU7s for those of us with original Gibbos?
Keep us posted. Use 12AX7s and leave the 6EU7s for those of us with original Gibbos?
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: Gibson GA15-RVT
Hi Dan,
I want to encourage you to contact Accutronics again. I sent email at 11AM and had a firm reply with a part number at 3PM, along with a pile of contact info. He said he had a "note" about my particular amp and maybe he doesn't know about the Falcon, though, many more of those were made.
emal here: info@accutronicsreverb.com
I'd be willing to bet it's the same tank for all the Gibsons of that era. The one I need is a 4FB2A1B and if you look on the Accutronics website, it will tell you exactly what that p/n means.
As for those 6EU7's, it may really depend on what I can scrape up from the existing tube stock. I'm I'm lucky, maybe those 12AX7EH will sound good in this circuit. They were awful in the 18W and the wreck. Far too bright.
What? Nothing to share on the power supply ladder and the PI? Even random thoughts are better than none!
Phil
I want to encourage you to contact Accutronics again. I sent email at 11AM and had a firm reply with a part number at 3PM, along with a pile of contact info. He said he had a "note" about my particular amp and maybe he doesn't know about the Falcon, though, many more of those were made.
emal here: info@accutronicsreverb.com
I'd be willing to bet it's the same tank for all the Gibsons of that era. The one I need is a 4FB2A1B and if you look on the Accutronics website, it will tell you exactly what that p/n means.
As for those 6EU7's, it may really depend on what I can scrape up from the existing tube stock. I'm I'm lucky, maybe those 12AX7EH will sound good in this circuit. They were awful in the 18W and the wreck. Far too bright.
What? Nothing to share on the power supply ladder and the PI? Even random thoughts are better than none!
Phil