Champ voltage question

jb1911 · December 17th, 2004, 06:59 PM

I just checked the voltages in my 1966 Champ and compared them to the schematic. They are all high. Pins 3 and 4 on the 6V6GT are supposed to be 350v and they are 400v. Pin 8 is supposed to be 19v and it's 25v. and so on for all the other voltages. Is this because when this amp was designed, you were lucky if you got 110 volts from your wall outlet, and now you get 124 volts, or is there something wrong with my amp? I'm supposed to be getting 330v from my filter caps and it's 380v. If there is something I can do to bring down the voltages, could someone let me in on it?

Joe-Bob · December 17th, 2004, 07:02 PM

Quote:

Originally Posted by jb1911

Is this because when this amp was designed, you were lucky if you got 110 volts from your wall outlet, and now you get 124 volts,

I thought that's was what the rectifier was for, no?

jb1911 · December 17th, 2004, 07:11 PM

The voltage coming out of the 5Y3GT is supposed to be 360v and it's 410.

Tremo · December 17th, 2004, 07:51 PM

There's nothing you can do, live with the voltage ya got. Use a JJ 6V6, it will handle the higher voltage and plate dissipation. Use only a NOS 5Y3. It will be fine.

Since the cathode voltage is 25 Volts, make sure the cathode bypass cap is a 50 volt unit.

lenny · December 17th, 2004, 07:53 PM

does it get crazy overdrive? do champs have adjustable bias? doesnt this mean its biased super "hot"?
just throwin out some ideas

jb1911 · December 17th, 2004, 08:18 PM

The 6V6GT is an RCA, the 5Y3GT is an RCA and I just gave it a cap job with Sprague Atoms @50v, so I guess I'm fine. I was checking the voltage because a couple of days ago I got 2 RCA 6V6GTs and I put one of them in the Champ. After two days the tube died. I have the other one in there now and it's been ok so far.

zook · December 17th, 2004, 10:21 PM

There's enough voltage to handle it, it will also draw more voltage so the readings will drop.

Winnie

jb1911 · December 18th, 2004, 08:21 AM

Quote:

Originally Posted by zook

try a 6L6 in there and see how you like it.

I have a 6L6 just laying here in front of me. If I put it in my Champ, what can I expect sound wise, and will I have to change anything else first?

LPBlue · December 18th, 2004, 10:33 AM

Quote:

Originally Posted by jb1911

Quote:

Originally Posted by zook

try a 6L6 in there and see how you like it.

I have a 6L6 just laying here in front of me. If I put it in my Champ, what can I expect sound wise, and will I have to change anything else first?

You should be safe using a 6L6, I do it all the time for different sounds. The 6L6 will have a harder edge to the sound with glassier highs than the 6V6. In the Champ circuit a 6L6 would like to see an 8 ohm spkr. but it isn'r critical.BTW, check your post over on HC, I posted a very effective way to tame the higher voltages we have today as opposed to when the older amps were made.

jjmantele · December 18th, 2004, 12:13 PM

I believe the power transformer was changed from the AA764 to the (hypothetical) AB764 Champ schematic. (Don't go by code on tube chart.) I cannot prove this on the "normal" champ since I cannot find a AB764 schematic for the Champ. I can only find one for the Vibro Champ and Bronco.

The change was to a higher voltage power tranny that puts out "365vac" on each leg to the rectifier plates instead of the "315vac" under the AA764. This creates higher DC voltages especially on the 6v6. The higher voltage setup uses a 40-20-20 cap can instead of the 20-20-20 on the AA764.

Watch out for bogus 6v6 plate & screen voltages on AB764 (VC/Bronco) schemes. Someone wrote in the AA764's 6v6 plate voltages on a AB764 scheme since they were not listed from the factory scheme. This doctored scheme is published in some popular books and web sites. It shows 340VDC and 410VDC on the exact same wire at the same time (6v6's screen.)

Wally · December 18th, 2004, 01:02 PM

JB1911, could you give the tranny codes off of that power transformer. JJmantele's post has me wanting to add that number to my reference list of transformer codes. The AA764 Champ used a 125P1B/022772 PT. I would like to know the code for the AB764 if it is different. JJmantele, if you have that code for the AB764 PT, could you post it back? Thanks to all... 8)
Wally

jhundt · December 18th, 2004, 03:21 PM

It's from 1966, and it hasn't blown up yet. Voltage measurements - what do they actually mean? If it works, and has been working for 38 years, the voltages are probably OK. And apparently the transformers and tubes don't mind either.

jb1911 · December 18th, 2004, 03:29 PM

Quote:

Originally Posted by jhundt

It's from 1966, and it hasn't blown up yet. Voltage measurements - what do they actually mean? If it works, and has been working for 38 years, the voltages are probably OK. And apparently the transformers and tubes don't mind either.

That is the reason I started this thead. It's burned out a power tube and a preamp tube since I got it.

LPBlue · December 18th, 2004, 03:49 PM

Since HC is down for the day, here's the link I posted there to make a great little voltage adapter to deal with the modern voltage/older amp problems.

http://www.geofex.com/Article_Folder...t/vintvolt.htm

I built one myself for use with an old Champ and would highly recommend it 8)

jjmantele · December 18th, 2004, 05:38 PM

Remember the voltage on the heaters matters. You don't want to lower all the voltages if that puts the heaters below the intended 6.3 or so.

The power transformer codes I show on the AB764 VC/Bronco:

Dual primary: 010020 (has 4 input wires for 117/234)
I have this one since there are 2 wires
going to each main line for 117v

Single primary:022772

My '74 VC had ~400v on the plate and ~25v on the cathode also. This ends up being about 22 watts idle. The AB764 scheme implies almost 19watts. "Official" max DC for class A is 14 (I think.) The AA Scheme implies 13.5watts idle.

I increased the cathode resistor to 516 from 449 ohms and now it idles at 17watts. I'm using an NOS RCA. I may go with a 740 ohm. The plate is not red at all so it's "ok."

Cooling down the idle of the 6v6 raises the plate voltage BTW. It probably came with a 25v cathode cap. It should be upgraded to a 50v if not done already.

Wally · December 18th, 2004, 06:07 PM

jhundt wrote: "It's from 1966, and it hasn't blown up yet. Voltage measurements - what do they actually mean? If it works, and has been working for 38 years, the voltages are probably OK. And apparently the transformers and tubes don't mind either."
Good advice until weak components take out a tranny or one's ears want to hear the amp as it should sound, imho. Old amps may work, but they don't function up to original specs and sonic quality with weak electrolytics. At least, that is my experience. Caps provide the basis upon everything else functions. I recently bought a SFDR for
ridiculously low bucks. Someone had been scavenging parts from it at a music store because it didn't work. The only real reason why it had been set aside was someone's inability to realize that it needed a new electrolytic bias cap that retails for $3.00 or less. I replaced all electrolytics, put in soem old US tubes, and the thing is a great amp. IF I sold it for 100% profit someone would get a steal. IMHO, replace the caps and then start analyzing the status of everything else.

LPBlue · December 18th, 2004, 06:11 PM

Quote:

Originally Posted by jhundt

It's from 1966, and it hasn't blown up yet.

Every amp that blew up today worked perfectly yesterday

Wally · December 18th, 2004, 06:36 PM

LPBlue, aint' it the truth? I've heard that sadly expressed too many times....."but it was workin' fine, and then it stopped working."
I have also heard people say their amp sounded just fine, when in actuality the bottom end was loose with out-of-tune subharmonics and the highs had no sparkle to them. The sonics go long before the caps quit working totally. One rough analogy would be the electric/acoustic that I heard 'fizzing' today. The battery was getting low, and the sound showed it. Caps act like batteries in that they provide the voltage. If the voltages aren't not good, steady and ready at the call, things don't work or sound very good.

jb1911 · December 18th, 2004, 06:42 PM

Hey Wally, thank's for the advice. I stated earlier that I gave it a cap job with Sprague Atoms at 50v. I also replaced the cap can. Everything else is original on the circuit board. I have these 2 brown lump caps ( .047 and .1 ) on the right side of the circuit board. Are these the chocolate drop caps that I have heard about? If I replace them with orange drops or Mallory 150s will it improve the tone?

Wally · December 18th, 2004, 07:05 PM

I apologize for that oversight on my part. I guess the week has been too long for me. Good luck with it.

jb1911 · December 18th, 2004, 08:25 PM

I have these 2 brown lump caps ( .047 and .1 ) on the right side of the circuit board. Are these the chocolate drop caps that I have heard about? If I replace them with orange drops or Mallory 150s will it improve the tone?

jhundt · December 19th, 2004, 03:50 AM

I was a little too quick when I said "just play it!". I didn't realize you were having problems, I thought you were just worrying about the voltage readings.

No one has commented much on your question about the differences in AC voltage available in 1966 vs. today (110 - 127). I think that is quite possibly a cause for the higher readings at every point in the amp, but I'm no electrical engineer.

My old Fender schematics all have this note: voltages read to ground with electronic voltmeter, values shown + or - 20% So you're still in range. Doesn't the type of meter affect readings, too? I thought that DMM's load the circuit way less than those older volt meters. Anyone here know about that?

jb1911 · December 19th, 2004, 07:53 AM

I have an RCA 5Y3GT, an RCA 6V6GT, and a Mullard 12ax7 in this amp. The cap can is a month old and I changed the 3 other electrolytics to Sprague Atoms @ 50v. I am thinking of doing the screen grid resistor and changing my bias resistor to 1K ( it is now reading 510 ohms ). What type of resistors do I need in these 2 spots and what brand do you all suggest?

I also have these 2 brown lump caps ( .047 and .1 ) on the right side of the circuit board. Are these the chocolate drop caps that I have heard about? If I replace them with orange drops or Mallory 150s will it improve the tone?

jjmantele · December 19th, 2004, 12:58 PM

Quote:

Originally Posted by jb1911

...The cap can is a month old and I changed the 3 other electrolytics to Sprague Atoms @ 50v. I am thinking of doing the screen grid resistor and changing my bias resistor to 1K ( it is now reading 510 ohms ). What type of resistors do I need in these 2 spots and what brand do you all suggest?

I also have these 2 brown lump caps ( .047 and .1 ) on the right side of the circuit board. Are these the chocolate drop caps that I have heard about? If I replace them with orange drops or Mallory 150s will it improve the tone?

Was the original cap can 20-20-20 or 40-20-20? The second one is the higher voltage circuit.

The 6v6 cathode resistor dissipates about 1watt. The AA764 says use a 1wt and the AB764 says use a 2wt. I used a 5 watt but would recommend either a 2 or 3 or 5wt.

My added screen resistor is dissipating about 0.01 watts. I would suggest a 1wt since I think this location could be subject to a wide range of possible current under different surroundings.

I changed out the chocolate drops for orange drops in my SFDR. I didn't notice a change. I didn't have my recording setup on my PC at the time so I couldn’t' do an objective "before and after." Some say it can be a night and day difference. I think there are too many variables to be able to predict the result. It's worth a try since they're cheap enough. Your results will vary.

jb1911 · December 19th, 2004, 03:13 PM

The can I replaced was a 20 20 20 Mallory. I don't know if it was the original one. It was in pretty good shape and there was no hum at all before I changed it. I still have it because I suspect it was fairly new. Good point about caps being so cheap. I'm thinking of trying the orange drops and the Mallory 150s. If there is no difference, I'm out 5 bucks and a half hour of my time. I like fiddling around anyway.

December 17th, 2004, 06:59 PM	#1 (permalink)
jb1911 TDPRI Member Join Date: Jun 2004 Location: Chicago area Posts: 92	Champ voltage question I just checked the voltages in my 1966 Champ and compared them to the schematic. They are all high. Pins 3 and 4 on the 6V6GT are supposed to be 350v and they are 400v. Pin 8 is supposed to be 19v and it's 25v. and so on for all the other voltages. Is this because when this amp was designed, you were lucky if you got 110 volts from your wall outlet, and now you get 124 volts, or is there something wrong with my amp? I'm supposed to be getting 330v from my filter caps and it's 380v. If there is something I can do to bring down the voltages, could someone let me in on it?

December 17th, 2004, 10:21 PM	#7 (permalink)
zook Tele-Holic Join Date: Aug 2003 Location: Northeast Kingdom, Vermont Posts: 833	try a 6L6 in there and see how you like it. There's enough voltage to handle it, it will also draw more voltage so the readings will drop. Winnie __________________ I have noticed that happy people are often evaluating themselves and unhappy people are always evaluating others. -William Glasser

December 18th, 2004, 12:13 PM	#10 (permalink)
jjmantele Tele-Holic Join Date: Aug 2003 Location: New Jersey Posts: 851	Power transformer I believe the power transformer was changed from the AA764 to the (hypothetical) AB764 Champ schematic. (Don't go by code on tube chart.) I cannot prove this on the "normal" champ since I cannot find a AB764 schematic for the Champ. I can only find one for the Vibro Champ and Bronco. The change was to a higher voltage power tranny that puts out "365vac" on each leg to the rectifier plates instead of the "315vac" under the AA764. This creates higher DC voltages especially on the 6v6. The higher voltage setup uses a 40-20-20 cap can instead of the 20-20-20 on the AA764. Watch out for bogus 6v6 plate & screen voltages on AB764 (VC/Bronco) schemes. Someone wrote in the AA764's 6v6 plate voltages on a AB764 scheme since they were not listed from the factory scheme. This doctored scheme is published in some popular books and web sites. It shows 340VDC and 410VDC on the exact same wire at the same time (6v6's screen.) __________________ JJman If it says "Vintage" on it -it isn't.

December 18th, 2004, 01:02 PM	#11 (permalink)
Wally Friend of Leo's Join Date: Mar 2003 Location: Lubbock, TX Posts: 4,212	PT info needed JB1911, could you give the tranny codes off of that power transformer. JJmantele's post has me wanting to add that number to my reference list of transformer codes. The AA764 Champ used a 125P1B/022772 PT. I would like to know the code for the AB764 if it is different. JJmantele, if you have that code for the AB764 PT, could you post it back? Thanks to all... 8) Wally

December 18th, 2004, 03:21 PM	#12 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	Just play it ! It's from 1966, and it hasn't blown up yet. Voltage measurements - what do they actually mean? If it works, and has been working for 38 years, the voltages are probably OK. And apparently the transformers and tubes don't mind either.

December 17th, 2004, 07:11 PM	#3 (permalink)
jb1911 TDPRI Member Join Date: Jun 2004 Location: Chicago area Posts: 92	The voltage coming out of the 5Y3GT is supposed to be 360v and it's 410.

December 17th, 2004, 07:51 PM	#4 (permalink)
Tremo Banned Friend of Leo's Join Date: Mar 2003 Location: Silicon Valley, CA, USA Posts: 3,803	There's nothing you can do, live with the voltage ya got. Use a JJ 6V6, it will handle the higher voltage and plate dissipation. Use only a NOS 5Y3. It will be fine. Since the cathode voltage is 25 Volts, make sure the cathode bypass cap is a 50 volt unit.

December 17th, 2004, 07:53 PM	#5 (permalink)
lenny Banned Friend of Leo's Join Date: Jan 2004 Location: New Haven, CT. USA Posts: 3,219	does it get crazy overdrive? do champs have adjustable bias? doesnt this mean its biased super "hot"? just throwin out some ideas

December 17th, 2004, 08:18 PM	#6 (permalink)
jb1911 TDPRI Member Join Date: Jun 2004 Location: Chicago area Posts: 92	The 6V6GT is an RCA, the 5Y3GT is an RCA and I just gave it a cap job with Sprague Atoms @50v, so I guess I'm fine. I was checking the voltage because a couple of days ago I got 2 RCA 6V6GTs and I put one of them in the Champ. After two days the tube died. I have the other one in there now and it's been ok so far.

December 18th, 2004, 03:49 PM	#14 (permalink)
LPBlue Tele-Meister Join Date: Jul 2003 Location: Markdale Ontario...oot in the woods Age: 52 Posts: 267	Modern voltage/older amps Since HC is down for the day, here's the link I posted there to make a great little voltage adapter to deal with the modern voltage/older amp problems. http://www.geofex.com/Article_Folder...t/vintvolt.htm I built one myself for use with an old Champ and would highly recommend it 8) __________________ It didn't make that smell when it was new, PULL THE PLUG!

December 18th, 2004, 05:38 PM	#15 (permalink)
jjmantele Tele-Holic Join Date: Aug 2003 Location: New Jersey Posts: 851	Voltage Remember the voltage on the heaters matters. You don't want to lower all the voltages if that puts the heaters below the intended 6.3 or so. The power transformer codes I show on the AB764 VC/Bronco: Dual primary: 010020 (has 4 input wires for 117/234) I have this one since there are 2 wires going to each main line for 117v Single primary:022772 My '74 VC had ~400v on the plate and ~25v on the cathode also. This ends up being about 22 watts idle. The AB764 scheme implies almost 19watts. "Official" max DC for class A is 14 (I think.) The AA Scheme implies 13.5watts idle. I increased the cathode resistor to 516 from 449 ohms and now it idles at 17watts. I'm using an NOS RCA. I may go with a 740 ohm. The plate is not red at all so it's "ok." Cooling down the idle of the 6v6 raises the plate voltage BTW. It probably came with a 25v cathode cap. It should be upgraded to a 50v if not done already. __________________ JJman If it says "Vintage" on it -it isn't.

December 18th, 2004, 06:07 PM	#16 (permalink)
Wally Friend of Leo's Join Date: Mar 2003 Location: Lubbock, TX Posts: 4,212	jhundt wrote: "It's from 1966, and it hasn't blown up yet. Voltage measurements - what do they actually mean? If it works, and has been working for 38 years, the voltages are probably OK. And apparently the transformers and tubes don't mind either." Good advice until weak components take out a tranny or one's ears want to hear the amp as it should sound, imho. Old amps may work, but they don't function up to original specs and sonic quality with weak electrolytics. At least, that is my experience. Caps provide the basis upon everything else functions. I recently bought a SFDR for ridiculously low bucks. Someone had been scavenging parts from it at a music store because it didn't work. The only real reason why it had been set aside was someone's inability to realize that it needed a new electrolytic bias cap that retails for $3.00 or less. I replaced all electrolytics, put in soem old US tubes, and the thing is a great amp. IF I sold it for 100% profit someone would get a steal. IMHO, replace the caps and then start analyzing the status of everything else.

December 18th, 2004, 06:36 PM	#18 (permalink)
Wally Friend of Leo's Join Date: Mar 2003 Location: Lubbock, TX Posts: 4,212	LPBlue, aint' it the truth? I've heard that sadly expressed too many times....."but it was workin' fine, and then it stopped working." I have also heard people say their amp sounded just fine, when in actuality the bottom end was loose with out-of-tune subharmonics and the highs had no sparkle to them. The sonics go long before the caps quit working totally. One rough analogy would be the electric/acoustic that I heard 'fizzing' today. The battery was getting low, and the sound showed it. Caps act like batteries in that they provide the voltage. If the voltages aren't not good, steady and ready at the call, things don't work or sound very good.

December 18th, 2004, 06:42 PM	#19 (permalink)
jb1911 TDPRI Member Join Date: Jun 2004 Location: Chicago area Posts: 92	Hey Wally, thank's for the advice. I stated earlier that I gave it a cap job with Sprague Atoms at 50v. I also replaced the cap can. Everything else is original on the circuit board. I have these 2 brown lump caps ( .047 and .1 ) on the right side of the circuit board. Are these the chocolate drop caps that I have heard about? If I replace them with orange drops or Mallory 150s will it improve the tone?

December 18th, 2004, 07:05 PM	#20 (permalink)
Wally Friend of Leo's Join Date: Mar 2003 Location: Lubbock, TX Posts: 4,212	I apologize for that oversight on my part. I guess the week has been too long for me. Good luck with it.

December 18th, 2004, 08:25 PM	#21 (permalink)
jb1911 TDPRI Member Join Date: Jun 2004 Location: Chicago area Posts: 92	I have these 2 brown lump caps ( .047 and .1 ) on the right side of the circuit board. Are these the chocolate drop caps that I have heard about? If I replace them with orange drops or Mallory 150s will it improve the tone?

December 19th, 2004, 03:50 AM	#22 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	jb 1911 and Wally - you're right I was a little too quick when I said "just play it!". I didn't realize you were having problems, I thought you were just worrying about the voltage readings. No one has commented much on your question about the differences in AC voltage available in 1966 vs. today (110 - 127). I think that is quite possibly a cause for the higher readings at every point in the amp, but I'm no electrical engineer. My old Fender schematics all have this note: voltages read to ground with electronic voltmeter, values shown + or - 20% So you're still in range. Doesn't the type of meter affect readings, too? I thought that DMM's load the circuit way less than those older volt meters. Anyone here know about that?

December 19th, 2004, 07:53 AM	#23 (permalink)
jb1911 TDPRI Member Join Date: Jun 2004 Location: Chicago area Posts: 92	I have an RCA 5Y3GT, an RCA 6V6GT, and a Mullard 12ax7 in this amp. The cap can is a month old and I changed the 3 other electrolytics to Sprague Atoms @ 50v. I am thinking of doing the screen grid resistor and changing my bias resistor to 1K ( it is now reading 510 ohms ). What type of resistors do I need in these 2 spots and what brand do you all suggest? I also have these 2 brown lump caps ( .047 and .1 ) on the right side of the circuit board. Are these the chocolate drop caps that I have heard about? If I replace them with orange drops or Mallory 150s will it improve the tone?

December 19th, 2004, 03:13 PM	#25 (permalink)
jb1911 TDPRI Member Join Date: Jun 2004 Location: Chicago area Posts: 92	The can I replaced was a 20 20 20 Mallory. I don't know if it was the original one. It was in pretty good shape and there was no hum at all before I changed it. I still have it because I suspect it was fairly new. Good point about caps being so cheap. I'm thinking of trying the orange drops and the Mallory 150s. If there is no difference, I'm out 5 bucks and a half hour of my time. I like fiddling around anyway.