GA-5 versus 5F1 Champ?

JohnnyCrash · August 16th, 2007, 04:18 AM

OK, I've got a ton of caps, resistors, and tube sockets left over.

I'm extremely tempted to go mad and have a Single Ended amp blowout to see how they all differ.

I'm looking at a Gibson GA-5
And a Kalamazoo Model-1 (sorta like an Epi VJr except not cheap chinese stuff)

If I choose to do this, I will put them all in combo cabs, they will all use Diode/SS rectifiers, and the same exact OT, and each will get a Jensen Neo 10-100 speaker. Trannies and Speakers I get wholesale, so that shouldn't hurt too badly.

I will try to get the voltages to what the originals had as well as using similar component values wherever possible. Otherwise, shielded wire will be the only thing the originals didn't have that mine will (and SS rects).

After all of the amps I've built from scratch, I can build a single ender in about a day... I guess I can build em and have a shootout + review.

Anybody have any experience with original GA-5's and Kalamazoo Model-1's? How do they compare with the Champ?

I know the K1 doesn't have NegFeedback and I think it has lower voltages than the EpiVJr, while the GA-5's NegFeedback is 47k instead of the 5F1 Champ's 22k (and the BF/SF Champ's 2700)... otherwise, how do these amps respond and sound in comparison?

I think I'll get to work :)

Natstrat79 · August 16th, 2007, 06:45 AM

I have a 1957 GA-5 that I can open up if you want. I haven't had the chance to directly compare it to a 5F1 but from what I've heard the GA-5's can be hotter and a little crunchier. Which is probably partly due to the fact that they have 220k on the 12ax7 plates versus the champs 100k. My GA-5 matches the schematic I found on the internet except for the filter caps were 20uf 20uf 10uf. I know Gibson was notorious for not following their own schematics but this little GA-5 is dead on except for the filter caps mentioned before.

Natstrat79 · August 16th, 2007, 06:49 AM

Another fun comparison could be early GA-6 versus 5E3.

http://www.harpamps.com/gibson/pg_0095.jpg

tele-martini · August 16th, 2007, 10:36 AM

That would be an extremely interesting comparison. As far as the 5F1 & the GA5 is concerned what would you use for tranny's? Can you get new tranny's to the exact spec the originals were?

JohnnyCrash · August 16th, 2007, 12:12 PM

Quote:

Originally Posted by tele-martini

That would be an extremely interesting comparison. As far as the 5F1 & the GA5 is concerned what would you use for tranny's? Can you get new tranny's to the exact spec the originals were?

I don't plan on spending that much money to use vintage styled repros...

I was planning on using the same off-the-shelf OT for all three amps probably a 5-8 watt (maybe Heyboers)... with all of them using the same OT and speaker I figured I'd be able to compare the sound of the circuits better.

Natstrat79 · August 16th, 2007, 05:47 PM

Quote:

Originally Posted by JohnnyCrash

I don't plan on spending that much money to use vintage styled repros...

I was planning on using the same off-the-shelf OT for all three amps probably a 5-8 watt (maybe Heyboers)... with all of them using the same OT and speaker I figured I'd be able to compare the sound of the circuits better.

IMHO The output transformers are part of what make the Gibson sound. When compared to their fender counterparts the Gibson output transformers are somewhat undersized. My '56 GA-6 has slightly less treble and less bass and more grind than the tweed deluxe clone I built awhile ago. The GA-6 output transformer was about 25% smaller than the heyboer tweed deluxe clone. The reduced bandwith and output transformer saturation is part of what I felt made for a unique "Gibson" sound. I haven't compared the output transformer of my GA-5 to a tweed champ so all I can say is it sure looks tiny and I cant imagine the 5f1 wouldn't be bigger.

Dont get me wrong though I still think you have an interesting comparison ahead of you and there's really no reason to be so picky unless your really trying to clone a GA-5 spot on.

zook · August 16th, 2007, 06:49 PM

Johnny,

I've built a couple GA5s. I like them a lot. I can't tell you exactly why, but as previously mentioned, I think the 220K plate resistors and the 2.2K cathode resistors make the difference. Also the grid resistors on the input are 47K instaed of 68K. I also built then without a board, just used a couple terminal strips. You can build one in an afternoon.

Winnie

JohnnyCrash · August 17th, 2007, 03:19 AM

I think I'll drop the GA-5 and just go for a Kalamazoo Model-1 for now. Like the GA-5 its got 47k input resistors and 2.2k cathode resistors, but 100k plate resistors...

I've got an old '50s power tranny that'll give me the right voltages for it :)

Although... hell, might as well build the GA-5 too, I've got an extra Octal tube socket (won't need it for rectifiers, I'm going SS there). I'll drop the 5F1 Champ - I've built too many of those already. My next Champ will be a BF/SF with a Master Volume instead of the 220k... again, with a Jensen Neo 10-100.

August 16th, 2007, 04:18 AM	#1 (permalink)
JohnnyCrash Poster Extraordinaire Join Date: Mar 2005 Location: Lost Angeles and Orange County Posts: 7,128	GA-5 versus 5F1 Champ? OK, I've got a ton of caps, resistors, and tube sockets left over. I'm extremely tempted to go mad and have a Single Ended amp blowout to see how they all differ. I'm looking at a Gibson GA-5 And a Kalamazoo Model-1 (sorta like an Epi VJr except not cheap chinese stuff) If I choose to do this, I will put them all in combo cabs, they will all use Diode/SS rectifiers, and the same exact OT, and each will get a Jensen Neo 10-100 speaker. Trannies and Speakers I get wholesale, so that shouldn't hurt too badly. I will try to get the voltages to what the originals had as well as using similar component values wherever possible. Otherwise, shielded wire will be the only thing the originals didn't have that mine will (and SS rects). After all of the amps I've built from scratch, I can build a single ender in about a day... I guess I can build em and have a shootout + review. Anybody have any experience with original GA-5's and Kalamazoo Model-1's? How do they compare with the Champ? I know the K1 doesn't have NegFeedback and I think it has lower voltages than the EpiVJr, while the GA-5's NegFeedback is 47k instead of the 5F1 Champ's 22k (and the BF/SF Champ's 2700)... otherwise, how do these amps respond and sound in comparison? I think I'll get to work :)

August 16th, 2007, 06:49 PM	#7 (permalink)
zook Tele-Holic Join Date: Aug 2003 Location: Northeast Kingdom, Vermont Posts: 800	Johnny, I've built a couple GA5s. I like them a lot. I can't tell you exactly why, but as previously mentioned, I think the 220K plate resistors and the 2.2K cathode resistors make the difference. Also the grid resistors on the input are 47K instaed of 68K. I also built then without a board, just used a couple terminal strips. You can build one in an afternoon. Winnie __________________ I have noticed that happy people are often evaluating themselves and unhappy people are always evaluating others. -William Glasser

August 16th, 2007, 06:45 AM	#2 (permalink)
Natstrat79 Tele-Meister Join Date: Jul 2007 Location: Iowa Posts: 126	I have a 1957 GA-5 that I can open up if you want. I haven't had the chance to directly compare it to a 5F1 but from what I've heard the GA-5's can be hotter and a little crunchier. Which is probably partly due to the fact that they have 220k on the 12ax7 plates versus the champs 100k. My GA-5 matches the schematic I found on the internet except for the filter caps were 20uf 20uf 10uf. I know Gibson was notorious for not following their own schematics but this little GA-5 is dead on except for the filter caps mentioned before.

August 16th, 2007, 06:49 AM	#3 (permalink)
Natstrat79 Tele-Meister Join Date: Jul 2007 Location: Iowa Posts: 126	Another fun comparison could be early GA-6 versus 5E3. http://www.harpamps.com/gibson/pg_0095.jpg

August 16th, 2007, 10:36 AM	#4 (permalink)
tele-martini Tele-Holic Join Date: Sep 2006 Location: Hilton, NY Age: 49 Posts: 900 11 Photos	That would be an extremely interesting comparison. As far as the 5F1 & the GA5 is concerned what would you use for tranny's? Can you get new tranny's to the exact spec the originals were?

August 17th, 2007, 03:19 AM	#8 (permalink)
JohnnyCrash Poster Extraordinaire Join Date: Mar 2005 Location: Lost Angeles and Orange County Posts: 7,128	I think I'll drop the GA-5 and just go for a Kalamazoo Model-1 for now. Like the GA-5 its got 47k input resistors and 2.2k cathode resistors, but 100k plate resistors... I've got an old '50s power tranny that'll give me the right voltages for it :) Although... hell, might as well build the GA-5 too, I've got an extra Octal tube socket (won't need it for rectifiers, I'm going SS there). I'll drop the 5F1 Champ - I've built too many of those already. My next Champ will be a BF/SF with a Master Volume instead of the 220k... again, with a Jensen Neo 10-100.