Tweed Champ Mod Question

blondeonblonde · October 24th, 2003, 03:17 PM

I recently bought a Tweed champ, and I was talking with a friend, who happens to be a very clever builder/tech- He was telling me about a mod to do to a Tweed champ that sounds incredible-
I think i have this right:
Find the Cathode bias resistor, and and bridge a 10 MFD electrolytic across it-
He says it makes the amp just scream...
I was wondering if you guys have ever heard of this mod, and what it does exactly?
I've always thought that Tweed Champs did not need any mods, but this one sounded pretty simple and non-destructive... Any thoughts????

Tim Swartz · October 24th, 2003, 03:37 PM

There is already a 25uF cap there. Adding an additional 10uF cap would be pointless.

Wally · October 24th, 2003, 04:08 PM

Tim, if you are still watching this thread, what are your thoughts on the necessity for putting in a 470 ohm/1 watt screen resistor on the 5D1, 5E1, and 5F1 Champs?

BrianF · October 24th, 2003, 05:48 PM

resistor to ground that is located at the junction of where the feedback resistor is connected...

It is covered in this site...

http://www.tone-lizard.com/lesson10.htm

go that link and then scroll down the page...right next to the picture of the Tweed Fender amp...

JDO · October 24th, 2003, 08:33 PM

Quote:

Originally Posted by blondeonblonde

I recently bought a Tweed champ, and I was talking with a friend, who happens to be a very clever builder/tech- He was telling me about a mod to do to a Tweed champ that sounds incredible-
I think i have this right:
Find the Cathode bias resistor, and and bridge a 10 MFD electrolytic across it-
He says it makes the amp just scream...
I was wondering if you guys have ever heard of this mod, and what it does exactly?
I've always thought that Tweed Champs did not need any mods, but this one sounded pretty simple and non-destructive... Any thoughts????

if he's a knowledgable tech the only thing i think he could be talking about is the cathode bias resistor in the first gain stage. on the 5F1 schems it's not there but i've never actually heard of one that didn't have it. but he's right, if you're doesn't have it, it will make it scream. before they took it out, it was a 25/25. you could experiement with whatever value you wanted. just look at the board. all the way to the right is a resistor (either a 1k5 or an 820 - don't have the schem infront of me). if it has a cap in parallell with it, don't worry. if not, then put one in and see if you like it.

Tim Swartz · October 24th, 2003, 08:42 PM

Quote:

Tim, if you are still watching this thread, what are your thoughts on the necessity for putting in a 470 ohm/1 watt screen resistor on the 5D1, 5E1, and 5F1 Champs?

Not necessary with good (NOS) 6V6s. Any amp using current production 6V6s would be advised to bump of the screens (until they don't glow when you lean on 'em).

Jparris · October 24th, 2003, 09:36 PM

One of my favorite amps (5F1). Leave it as is, IMHO.

jparris

JDO · October 24th, 2003, 11:53 PM

Quote:

Originally Posted by Jparris

One of my favorite amps (5F1). Leave it as is, IMHO.

jparris

i don't doubt that statement at all but my question is "what is stock"? the schem has no 25/25 cathode by-pass cap on the first gain stage but it seems that the majority of these i've read about that have been opened up have that cap in place. is that something that a tech or hobbiest put in after the fact? is it something that got writen down and as soon as fender tried it out they desided they liked it with the cap in it? or did some get sent out before everyone could remember to not put the cap in? who knows. but it's possible to have two completely stock 5F1 side-by-side where one would have the by-pass cap and the other wouldn't. and if that's the case, i could tell you which one would scream more - the one with the cap. the reason the cap was removed was to try and improve headroom. the cap in place gives the AC a free ride (as stated by mark norwine) and slams the tube hard.

so, look at your champ, if it has the cap, there's not much else i think you should do. if it doesn't, play around with different values. try a 25, try a 10, shoot, try a 1 and see which you like best. the 5E1's had a 25/25 (which to be safe go ahead and do a 25/50) like most other tweeds so that will probably be what would sound the most like a tweed.

BrianF · October 25th, 2003, 01:00 AM

It has nothing to do with the preamp tube cathode bypass.

In involves adding a bypass cap to the 1500 ohm cathode resistor of the 12AX7 that drives the power tube. The mod involves connecting that cap with a switch so that you can use it as a lead boost function. I tried it momentarily on my 5F1 champ and it seemed to work as advertised.

Marky D. · October 25th, 2003, 02:53 AM

Ah - I've got to see if mine has this cap!

I bought a completely stock otherwise pristine '59 champ at a flea market about 10 years ago but I've been underwhelmed about it's tone - even w/ a new speaker. W/ a recap, different tubes, etc. still the same...blah.

I've played others of its era that sound better, but can't figure out why mine doesn't deliver - any hints?

blondeonblonde · October 25th, 2003, 04:19 AM

I appreciate the advice, I still do not have the amo in hand, but when I do, I will certainly check for that cap, and consider this mod, seems pretty simple-
Of course if the amp sounds magical stock, I will not touch it!
I've played quite a few tweed champs, I know a good one when I hear it (fingers crossed...)

October 24th, 2003, 03:17 PM	#1 (permalink)
blondeonblonde Tele-Meister Join Date: Mar 2003 Location: nyc Posts: 210	Tweed Champ Mod Question I recently bought a Tweed champ, and I was talking with a friend, who happens to be a very clever builder/tech- He was telling me about a mod to do to a Tweed champ that sounds incredible- I think i have this right: Find the Cathode bias resistor, and and bridge a 10 MFD electrolytic across it- He says it makes the amp just scream... I was wondering if you guys have ever heard of this mod, and what it does exactly? I've always thought that Tweed Champs did not need any mods, but this one sounded pretty simple and non-destructive... Any thoughts????

October 24th, 2003, 04:08 PM	#3 (permalink)
Wally Friend of Leo's Join Date: Mar 2003 Location: Lubbock, TX Posts: 3,988	Screen resistor? Tim, if you are still watching this thread, what are your thoughts on the necessity for putting in a 470 ohm/1 watt screen resistor on the 5D1, 5E1, and 5F1 Champs?

October 24th, 2003, 05:48 PM	#4 (permalink)
BrianF Friend of Leo's Join Date: Apr 2003 Location: Carlsbad, Ca Posts: 2,154 7 Photos	no...the 25 uF cap goes across the 1500 ohm resistor to ground that is located at the junction of where the feedback resistor is connected... It is covered in this site... http://www.tone-lizard.com/lesson10.htm go that link and then scroll down the page...right next to the picture of the Tweed Fender amp...

October 24th, 2003, 09:36 PM	#7 (permalink)
Jparris Tele-Meister Join Date: Mar 2003 Location: Valdosta, Georgia Posts: 133	Man, Tweed Champs scream STOCK!!! One of my favorite amps (5F1). Leave it as is, IMHO. jparris __________________ Richard Hell: "Musicians were being worshipped as idols and I thought that was pathetic and a lie. So I was undermining that -- wearing these beat up clothes & talking about real life, not romantic love songs and teenage clichés."

October 25th, 2003, 01:00 AM	#9 (permalink)
BrianF Friend of Leo's Join Date: Apr 2003 Location: Carlsbad, Ca Posts: 2,154 7 Photos	your missing the mod... It has nothing to do with the preamp tube cathode bypass. In involves adding a bypass cap to the 1500 ohm cathode resistor of the 12AX7 that drives the power tube. The mod involves connecting that cap with a switch so that you can use it as a lead boost function. I tried it momentarily on my 5F1 champ and it seemed to work as advertised.

October 24th, 2003, 03:37 PM	#2 (permalink)
Tim Swartz Tele-Afflicted Join Date: Mar 2003 Location: Michigan - Tweenst the Great Lakes Posts: 1,881	There is already a 25uF cap there. Adding an additional 10uF cap would be pointless.

October 25th, 2003, 02:53 AM	#10 (permalink)
Marky D. Tele-Meister Join Date: Mar 2003 Location: Minneapolis, MN Age: 47 Posts: 314	25-25 cap Ah - I've got to see if mine has this cap! I bought a completely stock otherwise pristine '59 champ at a flea market about 10 years ago but I've been underwhelmed about it's tone - even w/ a new speaker. W/ a recap, different tubes, etc. still the same...blah. I've played others of its era that sound better, but can't figure out why mine doesn't deliver - any hints?

October 25th, 2003, 04:19 AM	#11 (permalink)
blondeonblonde Tele-Meister Join Date: Mar 2003 Location: nyc Posts: 210	Interesting replies I appreciate the advice, I still do not have the amo in hand, but when I do, I will certainly check for that cap, and consider this mod, seems pretty simple- Of course if the amp sounds magical stock, I will not touch it! I've played quite a few tweed champs, I know a good one when I hear it (fingers crossed...)