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Roodboy
09-21-2006, 07:25 PM
Can anyone fill me in on the differences between the two? I think the dripface silvers are the same as the blackfaces.
I'm looking for a Jamesgang/Joe Walsh Funk 49 vibe.
Thanks

QuickDraw
09-21-2006, 10:01 PM
as far as i know the faceplate and grille cloth are different and that's it on the champs

Gas-man
09-22-2006, 08:25 AM
I've had both and to my ears the blackface had smoother OD than the silver.

Silver was somewhat buzzy.

utterhack
09-22-2006, 02:40 PM
I've had both and to my ears the blackface had smoother OD than the silver.

Silver was somewhat buzzy.

Since there were no circuit changes, I'd chalk that up more to the differences between two old amps than the difference between blackface and silverface champs.

TopJimmy5150
09-22-2006, 03:11 PM
Post '72 SF Champs have plywood construction. I think there were some changes in the OT, but nothing terrible. I'm sure at one point they probably eliminated cloth wires and other running changes that effected the whole line, but in general the Champs/Vibro Champs didn't screwed around with too much by the CBS penny-pinchers. I have a '76 that's not going anywhere. :D

jonny guitar
09-22-2006, 03:59 PM
Buzzy??? Wow, my SF champ could be decribes in many ways but I would never call it buzzy in the least.

As to the original posters quest for james gang...decent boost pedal and sf champ will just totally nail it!!

Dana-L
10-15-2006, 01:04 PM
Can anyone fill me in on the differences between the two? I think the dripface silvers are the same as the blackfaces.
I'm looking for a Jamesgang/Joe Walsh Funk 49 vibe.
ThanksFrom what I can tell from the schematics, in the Silverface era Fender changed the specifications on the power transformer so they provide higher voltages. Otherwise, the schematics are identical. The difference is that the potential nearest the rectifier is listed as 420V for Silverface Champs versus 360V for the Blackface versions.

On the schematics, the part numbers for the power transformers remain unchanged (125P1B) but the listed voltages have changed.

Do any amp experts have any insight on this?

Specifically, would adding a dropping resistor between the power transformer and first PS filter cap be all it takes to convert a Silverface Champ to Blackface specifications?

Also, on my own Silverface Champ, I've also noticed that the first power filter cap (inside the silver aluminum cap can) is actually 40uF whereas the schematic says it should be only 20uF.

Very best regards,

-Dana

marscottm
10-15-2006, 01:32 PM
it was my understanding that PT changes only affected the larger amps (i.e. bigger than a Deluxe). I doubt there's any significant difference between a BF and SF champ PT

Scott

billyguitar
10-15-2006, 03:19 PM
I had read Funk 49 was an Esquire or Tele and a Deluxe. Not a fan of champs myself even though I have two tweeds, a blackface and a Bronco which is a vibrochamp. I think other little amps sound better, for the most part. Gibsons, Kays, Silvertones etc.. Just my opinion, not dissing anyone's taste in amps. Afterall, if we all liked the same stuff we'd all sound the same!

drbob1
10-15-2006, 03:41 PM
I've owned 5 or so Vibrochamps and champs, no difference at all in sound. The best sounding one I have is an early 70s SF.

Dana-L
10-15-2006, 03:51 PM
it was my understanding that PT changes only affected the larger amps (i.e. bigger than a Deluxe). I doubt there's any significant difference between a BF and SF champ PT

ScottLooking even more closely at the Blackface and Silverface schematics, the PT voltages feeding the 5Y3 rectifier increased from 320V AC (Blackface) to 365V AC (Silverface).

The only change I see is the increase in power supply voltages; Other than a three prong cord, a thermal protector, and a 0.047 uF cap (all on the input side of the PT), every single resistor and capacitor value on the schematic is the same for the Blackface and Silverface Champ amps.

What else could cause the increase in voltage other than changed specifications for the power transformer?

Best,

-Dana

marshallnoise
10-15-2006, 03:58 PM
I love my SF Champ. It is a 73 and its blowing fuses. But I think its because I am running it through an 8 ohm load. Any guys think that might do it?

Dana-L
10-15-2006, 04:19 PM
I love my SF Champ. It is a 73 and its blowing fuses. But I think its because I am running it through an 8 ohm load. Any guys think that might do it?I'm an SF Champ lover, too. Mine's an '80 or '81 that I got new as a Christmas gift from my mom and dad.

I don't know if running an 8 Ohm load would cause fuses to fail but it will eventually kill your output transformer.

What I did was build some cables and a small junction box (with parts from Radio Shack) that allows me to connect a Jensen P10R and P15R (each is rated at 8 Ohms) in parallel (for a net 4 Ohm load) to the Champ's 3.2 Ohm output (a safe impedance mismatch).

The result is very, very good (to put it mildly)!

-Dana

marshallnoise
10-15-2006, 04:26 PM
I'm an SF Champ lover, too. Mine's an '80 or '81 that I got new as a Christmas gift from my mom and dad.

I don't know if running an 8 Ohm load would cause fuses to fail but it will eventually kill your output transformer.

What I did was build some cables and a small junction box (with parts from Radio Shack) that allows me to connect a Jensen P10R and P15R (each is rated at 8 Ohms) in parallel (for a net 4 Ohm load) to the Champ's 3.2 Ohm output (a safe impedance mismatch).

The result is very, very good (to put it mildly)!

-Dana.

Schematic!!!!! Puhlease!!!!!!!!!!

Texsunburst59
10-15-2006, 04:49 PM
Here's a copy of the SF Champ schematic & chassis layout.

http://www.ampwares.com/ffg/schem/champ_aa764_schem.gif
http://www.ampwares.com/ffg/schem/champ_5f1_layout.gif

Dana-L
10-15-2006, 04:54 PM
.

Schematic!!!!! Puhlease!!!!!!!!!!The pre-CBS schematics are available here:

http://www.ampwares.com/ffg/schematics.html

Here's the CBS version:

http://mysite.verizon.net/koitopia/ChampSilverface.gif

Have fun!

-Dana

Dana-L
10-15-2006, 05:49 PM
.

Schematic!!!!! Puhlease!!!!!!!!!!I don't have a schematic for the junction box pictured below - it's just three 1/4 phono jacks wired so all the tips are connected to one another and all the sleeves are connected to one another using short pieces of stranded wire.

The twisted wires have a male RCA plug on the end that connects to the Champ and a standard 1/4" phone plug that goes into the black junction box. Each of the remaining jacks are used to connect to the 8 Ohm speakers.

I got the box and jacks at Radio Shack. The RCA and phone plug are made by Neutrik and came from Parts Express (http://www.partsexpress.com (http://www.partsexpress.com/)). You could get similar items at Radio shack.

Building these was good soldering practice for me.

-Dana

http://mysite.verizon.net/koitopia/ChampCableBox-02.jpg

marshallnoise
10-15-2006, 08:58 PM
I don't have a schematic for the junction box pictured below - it's just three 1/4 phono jacks wired so all the tips are connected to one another and all the sleeves are connected to one another using short pieces of stranded wire.

The twisted wires have a male RCA plug on the end that connects to the Champ and a standard 1/4" phone plug that goes into the black junction box. Each of the remaining jacks are used to connect to the 8 Ohm speakers.

I got the box and jacks at Radio Shack. The RCA and phone plug are made by Neutrik and came from Parts Express (http://www.partsexpress.com (http://www.partsexpress.com/)). You could get similar items at Radio shack.

Building these was good soldering practice for me.

-Dana

http://mysite.verizon.net/koitopia/ChampCableBox-02.jpg

Man that is such a great idea. I want to do that but since all I am running my Champ through is a Marshall 1936 2X12 and that sorry cab only has 16 ohm speakers. I think I will just build a nice 1X12 extension cab for it. I already converted the RCA style jack to a regular 1/4" jack. I am sitting and looking at this thing and good gawd it is simple. Has HUGE resistors in it. I just hope all of them haven't left spec.

Thanks for posting that though, it gives me other ideas...

Wakarusa
10-15-2006, 09:57 PM
One very slight difference between blackface and silverface is the 330pF cap between power tube grid and ground on the silverface. In the real world I've seen this cap installed grid-cathode, plate to cathode, and in values ranging from 330pF to 2200pF. The earliest Champ I've seen it in is a '69 drip-edge.

Also (as John Philips has posted repeatedly) as the wall voltage crept up and the PT stayed the same, B+ crept up too -- making it so the 470 cathode resistor on the power tube often doesn't bias the tube correctly.

Dana-L
10-15-2006, 10:22 PM
One very slight difference between blackface and silverface is the 330pF cap between power tube grid and ground on the silverface. In the real world I've seen this cap installed grid-cathode, plate to cathode, and in values ranging from 330pF to 2200pF. The earliest Champ I've seen it in is a '69 drip-edge.

Also (as John Philips has posted repeatedly) as the wall voltage crept up and the PT stayed the same, B+ crept up too -- making it so the 470 cathode resistor on the power tube often doesn't bias the tube correctly.Nice catch on the 330pF cap! I missed that one.

Regarding wall voltage, what was the typical value in the early 1960's?

Do you think there is any merit to the idea of installing a dropping resistor between the rectifier and the first filter cap to reduce B+?

Finally, what value of cathode bias resistor do you prefer (assuming the higher B+ of the Silverface units)?

Thanks & best regards,

-Dana

marshallnoise
10-15-2006, 10:40 PM
Ok, are these amps supposed to have sprague atom caps and mallory caps in them?

Wakarusa
10-15-2006, 10:51 PM
Nice catch on the 330pF cap! I missed that one.

Regarding wall voltage, what was the typical value in the early 1960's?

Do you think there is any merit to the idea of installing a dropping resistor between the rectifier and the first filter cap to reduce B+?

Finally, what value of cathode bias resistor do you prefer (assuming the higher B+ of the Silverface units)?

Thanks & best regards,

-Dana

I didn't get my first multimeter until some time in the '70s, so couldn't say for sure :) Older schematics assume a line voltage as low as 117VAC. Modern line voltage runs around 124VAC.

I wouldn't bother with a dropping resistor. For the cathode resistor typical values are 870, 910, and 1K (varies a bit from amp to amp).

Wakarusa
10-15-2006, 10:59 PM
Ok, are these amps supposed to have sprague atom caps and mallory caps in them?

Not sure what you mean by "supposed to". The originals used a variety of brands of film caps and mostly Mallory electrolytics (brown paper wrapped in the older ones, white poly tubes in later ones). None that I know of would have come with Sprague Atoms as OEM equipment.

For replacements, the main filter cap is a multi-section can so the only equivalent in the Atom line would be to replace it with discretes. For the rest of the caps, anything you like with appropriate ratings will do - they don't "have" to be Mallory and Sprague.

Dana-L
10-15-2006, 11:10 PM
Ok, are these amps supposed to have sprague atom caps and mallory caps in them?In my early 80's Silverface, most of the caps on the board look similar to Sprague Orange Drops except that they are larger and are colored blue. There are also a couple of ceramic disc caps.

The smaller electrolytics are silver-colored and are all axial.

The filter cap can is a 40/20/20uF Mallory.

All the resistors are carbon comp.

-Dana

marshallnoise
10-15-2006, 11:14 PM
Not sure what you mean by "supposed to". The originals used a variety of brands of film caps and mostly Mallory electrolytics (brown paper wrapped in the older ones, white poly tubes in later ones). None that I know of would have come with Sprague Atoms as OEM equipment.

For replacements, the main filter cap is a multi-section can so the only equivalent in the Atom line would be to replace it with discretes. For the rest of the caps, anything you like with appropriate ratings will do - they don't "have" to be Mallory and Sprague.

It looks like mine has been messed with pretty hard then. It had a replacement power cable put in, I don't mind that at all.

I am having a hard time reading the schematics though. I am pretty much doing this blind as far as following the signal path and all that jazz. I have biased my old JCM800s before so I am well aware of the hazzards so I don't need that lecture. Its just hard. I wish there was a place I could learn what is happening electronically...

All I know is that the date stamped in the chasis is Mar 1 1973, which is pretty darn cool. It was made by L. Castillo too.

Dana-L
10-15-2006, 11:28 PM
I didn't get my first multimeter until some time in the '70s, so couldn't say for sure :) Older schematics assume a line voltage as low as 117VAC. Modern line voltage runs around 124VAC.

I wouldn't bother with a dropping resistor. For the cathode resistor typical values are 870, 910, and 1K (varies a bit from amp to amp).Thanks for your reply, Todd.

I'm still trying to figure out the source of the increased B+. Note that even the CBS schematic that I took from an early 70's Fender Service Manual shows a line voltage of 117V AC and a voltage feeding the rectifier of 365V AC (versus 320V AC on the pre-CBS schematic, the wall voltage is not noted).

Please excuse my electronics ignorance, but would one assume that if an input voltage of 117 resulted in an output of 365 that to get only 320 out of the transformer, you would need to feed it with only 103? (117/365 ~ 103/320).

Out of curiosity, I just checked the wall voltage in my house and it read 118.5V AC?! Maybe that's why I get such great vintage tone when I play at home but have such trouble trying to recreate it for an audience! ;)

Best regards,

-Dana

Dana-L
10-15-2006, 11:41 PM
I am having a hard time reading the schematics though. I am pretty much doing this blind as far as following the signal path and all that jazz. I have biased my old JCM800s before so I am well aware of the hazzards so I don't need that lecture. Its just hard. I wish there was a place I could learn what is happening electronically...I've found these books to be helpful:

http://www.amazon.com/Guitar-Amp-Handbook-Understanding-Amplifiers/dp/087930863X/sr=8-2/qid=1160973010/ref=sr_1_2/104-7801215-9091910?ie=UTF8&s=books

http://www.amazon.com/Tube-Amp-Book-Aspen-Pittman/dp/0879307676/sr=8-1/qid=1160973010/ref=sr_1_1/104-7801215-9091910?ie=UTF8&s=books

The first one I'd buy is the 'Guitar Amp Handbook' by Dave Hunter. If you like it, you'll automatically want the Pittman 'Tube Amp Book' (THE Classic reference, IMO, from the founder of Groove Tubes).

Have fun!

-Dana

marshallnoise
10-15-2006, 11:57 PM
I've found these books to be helpful:

http://www.amazon.com/Guitar-Amp-Handbook-Understanding-Amplifiers/dp/087930863X/sr=8-2/qid=1160973010/ref=sr_1_2/104-7801215-9091910?ie=UTF8&s=books

http://www.amazon.com/Tube-Amp-Book-Aspen-Pittman/dp/0879307676/sr=8-1/qid=1160973010/ref=sr_1_1/104-7801215-9091910?ie=UTF8&s=books

The first one I'd buy is the 'Guitar Amp Handbook' by Dave Hunter. If you like it, you'll automatically want the Pittman 'Tube Amp Book' (THE Classic reference, IMO, from the founder of Groove Tubes).

Have fun!

-Dana

Thanks!!! I am gonna get the first one right away.

So after checking everything in the amp...I went down stairs to plug it in and see what happens. Sure enough, the 6V6 lit up with a bright white light and the amp shut off, blowing another fuse. Glad its not a transformer. Any suggestions? Could I have a shorted tube?

Wakarusa
10-16-2006, 12:04 AM
Its just hard. I wish there was a place I could learn what is happening electronically...



You could start here.... :)

http://www.wakarusaamp.com/tmp_pix/237_3786small.jpg


On a (slightly) more serious note, it's tough to recommend reading without knowing where you're starting from.

Wakarusa
10-16-2006, 12:09 AM
I'm still trying to figure out the source of the increased B+. Note that even the CBS schematic that I took from an early 70's Fender Service Manual shows a line voltage of 117V AC and a voltage feeding the rectifier of 365V AC (versus 320V AC on the pre-CBS schematic, the wall voltage is not noted).

Please excuse my electronics ignorance, but would one assume that if an input voltage of 117 resulted in an output of 365 that to get only 320 out of the transformer, you would need to feed it with only 103? (117/365 ~ 103/320).

Out of curiosity, I just checked the wall voltage in my house and it read 118.5V AC?! Maybe that's why I get such great vintage tone when I play at home but have such trouble trying to recreate it for an audience! ;)



Don't take the schematic as absolute gospel. Not uncommon for the listed voltages to be +/- some outrageous amount, for some values to be updated over time while others are not, or for everything to rely on being measured with a meter with a much lower ohm/volt input impedance (think Simpson 260, not Fluke 87).

If you want to get 320VDC for B+ (and you've got ~360VDC now...) you're looking at a dropping resistor. Lowering line to 103VAC will probably run the heaters cold.

118 at the wall saves money on autotransformers for sure :)

marshallnoise
10-16-2006, 12:10 AM
You could start here.... :)

http://www.wakarusaamp.com/tmp_pix/237_3786small.jpg


On a (slightly) more serious note, it's tough to recommend reading without knowing where you're starting from.

Haha! Nice collection! Well, I understand all the symbols. I know what it looks like to have a cap in parallel to a resistor. But I don't know WHY you would do that. I think that book that was recommended to me earlier might be the ticket.

Thanks for the help!

Wakarusa
10-16-2006, 12:12 AM
Thanks!!! I am gonna get the first one right away.

So after checking everything in the amp...I went down stairs to plug it in and see what happens. Sure enough, the 6V6 lit up with a bright white light and the amp shut off, blowing another fuse. Glad its not a transformer. Any suggestions? Could I have a shorted tube?

You could have a shorted tube or a shorted output transformer or both. What makes you think the OT is good?

Wakarusa
10-16-2006, 12:17 AM
Haha! Nice collection! Well, I understand all the symbols. I know what it looks like to have a cap in parallel to a resistor. But I don't know WHY you would do that. I think that book that was recommended to me earlier might be the ticket.

Thanks for the help!

The REALLY cool ones are the Chaffee book and the two odd looking ones in upper right -- the latter are original RCA engineering handbooks for vacuum tubes -- much more thorough specs than the standard handbooks.

As for WHY different things are done in amplifiers, the cheapest/easiest place to start are the tech info pages generously written by Randall Aiken. http://www.aikenamps.com. Go to tech info, then advanced, then read the pages on "Designing Common Cathode Triode Amplifiers"

marshallnoise
10-16-2006, 12:28 AM
You could have a shorted tube or a shorted output transformer or both. What makes you think the OT is good?

Well, my only reason for thinking that is that when I remove the tube, the amp lights up just fine, the 12AX7 and the rectifier tube light up fine, and it doesn't blow fuses. And I know that tubes are not supposed to emit a white flash either!

:eek:

Wakarusa
10-16-2006, 12:38 AM
Well, my only reason for thinking that is that when I remove the tube, the amp lights up just fine, the 12AX7 and the rectifier tube light up fine, and it doesn't blow fuses. And I know that tubes are not supposed to emit a white flash either!

:eek:

I agree that the 6V6 is suspect. The OT may or may not be fine, since with the power tube pulled one end of the OT primary is disconnected from the circuit.

And some tubes do flash white when first powered on, but I've never seen a 6V6 that a) flashes and b) is good :)

(it's the heater filament that is flashing in the ones that do it normally)

marshallnoise
10-16-2006, 12:46 AM
I agree that the 6V6 is suspect. The OT may or may not be fine, since with the power tube pulled one end of the OT primary is disconnected from the circuit.

And some tubes do flash white when first powered on, but I've never seen a 6V6 that a) flashes and b) is good :)

(it's the heater filament that is flashing in the ones that do it normally)

LOL! You have a humorous way of putting things. What is funny is that I know I am surrounded by 40 somethings who have a lot more time under my belt than I do but I love it. I am only 25 and still learning about all this stuff. I plan on heading to Cal Poly SLO to get my Dual Masters degree in Business and Engineering. I already have the BBA but I should have gone to school for engineering since it is really the one thing I truly find sustained interest in.

I am reading Aiken's site right now and I imagine I will be on that site for quite a while. Thanks for the link and the know how!

The Champ was running fine for a while but it has the EH 6V6GT in it. It is what it came with when I bought it. I think I ought to buy a cheap one just to test and see if it is actually the tube or not. Fortunatley fuses are cheap but I know I would be gambling if I keep it up.

Thanks!

Paul :dude

Wakarusa
10-16-2006, 01:12 AM
The Champ was running fine for a while but it has the EH 6V6GT in it.
The EH 6V6GT is, IMHO, utter rubbish for reliability. No comment on how they sound as I've never seen one last long enough to really form an opinion ;)

Try a JJ/Tesla 6V6 in there.. affordable and in current production. That or you can whip up a quick rig to test the OT. Or throw in the towel and go see your local amp tech. An hour on the bench is probably cheaper than a good NOS 6V6 (and about twice the cost of the suggested JJ. Your mileage may vary of course). If you're nice (and he/she/it is any good) they might even show you what all the interesting bits do.

Jim S
02-27-2007, 11:29 PM
Trying to get the bottom line of the Champs. As I understand it...

Tweeds had 5E1 or 5F1 circuits
BF or SF champs had AA764 circuit

The sonic differences are subtle or not?