Fender Silverface Champ questions

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Post by ??????? » Tue Jan 04, 2011 10:09 pm

I've never noticed an impedance mismatch, by itself, to wreak an inordinate amount of havoc on the timbre of an amp. It can certainly reduce efficiency/loudness a bit. In extreme cases it can stress tubes and/or output transformer.

Now I HAVE heard individual speakers that made a given amp sound like shit, regardless of impedance. I think that from my perspective this would be a way bigger concern.

But that's just MY opinion/experience.

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Post by KennyLusk » Tue Jan 04, 2011 10:32 pm

Jim Williams wrote:When I bought my 1972 Vibro Champ, it also sounded like crap. The distortion was tizzy, the top end screechy and it hummed.

It came with the revered replacement "Jensen" speaker. That I hated, too tinny. I still have it if anyone wants it.

So I made it into something I like. First, out with the vibrato. I did a 2 stage preamp with treble, mid and bass controls. I added a master volume.
The speaker is an Eminence and sounds real smooth. I replaced the 1k 2 watt resistor in the power stage with a choke. That removed the hum.

Next, add some butt. I use a 6CA7 power tube, it's running at around 10~12 watts. I also removed the crappy can filter caps and replaced them with a pair of dual 100 uf 500 volters.

This amp screams. It drives a 4x12 loud enough for live gigs. Best harp amp ever too. Never pearcing, always fat and smooth. Does clean better too with the extra wattage.
Jim those are cool mod notes.

I'm curious why ditch the vibro?
I have a '76 vibro and wouldn't even consider pulling that section. Tube vibro?...it's such a wonderful thang.
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Post by ??????? » Wed Jan 05, 2011 6:47 am

I also think the tremolo in the vibro champ is a very good tremolo.

Unlike the optical tremolo in the larger blackface/silverface amps, the Vibro Champ and Princeton kept the bias-vary tremolo from earlier generations of Fender amps. This is a richer, less "ray-gun" tremolo that I prefer.

There was a time when tremolo wasn't too fashionable an effect. Many people sacrificed it in amps to make extra gain stages, etc. Then it came 'back in style' and those poor old amps had to go through getting completely un-modded to put back to original to re-gain some of their resale value. If extra holes or other butchery hasn't occurred, usually this can be done without issue.

Once upon a time, these weren't "vintage" amps. They were cheap and plentiful... especially something like a lowly champ. At one time, getting one of these to hack up was probably FAR cheaper than buying components for a new amp build (actually in some places, this is still probably true, but shhh!)

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Post by Matt C. » Wed Jan 05, 2011 7:12 am

so i think i'm going to get a new power tube and a new speaker for this amp and see how it does after that. for the speaker i'm looking at the weber signature series.

for tubes - is there a particularly reliable place online to order NOS tubes? i found a couple sites that seemed to have decent prices, but I was worried about potential sketchiness (probably an unfair judgement, based solely on their poorly designed websites...)

i'm excited to try modding the circuit too, but i don't wanna get too far ahead of myself.

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Post by ??????? » Wed Jan 05, 2011 7:30 am

mattcastore wrote:so i think i'm going to get a new power tube and a new speaker for this amp and see how it does after that. for the speaker i'm looking at the weber signature series.

for tubes - is there a particularly reliable place online to order NOS tubes? i found a couple sites that seemed to have decent prices, but I was worried about potential sketchiness (probably an unfair judgement, based solely on their poorly designed websites...)

i'm excited to try modding the circuit too, but i don't wanna get too far ahead of myself.
I like KCA NOS tubes. Mike Kropotkin owns it. He's a good guy. There are many other good tube retailers, too. Tube Depot, Tube Store... all of these places are reputable, and I've done business personally with them. I've never tried any others, but there are plenty of others that are reputable.

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Post by KennyLusk » Wed Jan 05, 2011 8:35 am

Antique Electronic Supply, aka http://tubesandmore.com/ is local here in the Phoenix area...not a sketchy operation. Reliable, reasonable, dependable shipping.
"The mushroom states its own position very clearly. It says, "I require the nervous system of a mammal. Do you have one handy?" Terrence McKenna

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Post by Jim Williams » Wed Jan 05, 2011 9:00 am

KennyLusk wrote:
Jim Williams wrote:When I bought my 1972 Vibro Champ, it also sounded like crap. The distortion was tizzy, the top end screechy and it hummed.

It came with the revered replacement "Jensen" speaker. That I hated, too tinny. I still have it if anyone wants it.

So I made it into something I like. First, out with the vibrato. I did a 2 stage preamp with treble, mid and bass controls. I added a master volume.
The speaker is an Eminence and sounds real smooth. I replaced the 1k 2 watt resistor in the power stage with a choke. That removed the hum.

Next, add some butt. I use a 6CA7 power tube, it's running at around 10~12 watts. I also removed the crappy can filter caps and replaced them with a pair of dual 100 uf 500 volters.

This amp screams. It drives a 4x12 loud enough for live gigs. Best harp amp ever too. Never pearcing, always fat and smooth. Does clean better too with the extra wattage.
Jim those are cool mod notes.

I'm curious why ditch the vibro?
I have a '76 vibro and wouldn't even consider pulling that section. Tube vibro?...it's such a wonderful thang.
Yes, for you. Me, I grew up in the early 1960's. I've heard enough cheesy pop songs with Fender vibrato on it to make me puke.

Then, in 1967, Jimi Hendrix told me to never listen to surf music again. I took his advice. I still have a hard time listening to Gilmore when he used it.

Along with ALL my vintage Fender amps, the Showmans, Deluxe Reverb's, etc, I removed both the vibrato and tank reverb circuits. I used the extra tube stage for more useful purposes. My amps have a tube based loop for my Lexicon reverbs. Some have different preamp designs. None have either vibrato or spring reverbs. Me happy.
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Post by jgimbel » Wed Jan 05, 2011 9:09 am

KennyLusk wrote:Antique Electronic Supply, aka http://tubesandmore.com/ is local here in the Phoenix area...not a sketchy operation. Reliable, reasonable, dependable shipping.
+1. I've never bought tubes from them, but that's where I've bought tolex for two cabs I built, one last year and one a few weeks ago. Their site does seem a little sketchy but they're great people there, good prices, and the tolex I ordered from them reached me all the way in Philadelphia only a few days later.
My first new personal album in four years - pay what you want - http://jessegimbel.bandcamp.com

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Post by KennyLusk » Wed Jan 05, 2011 9:21 am

Jim Williams wrote: Yes, for you. Me, I grew up in the early 1960's. I've heard enough cheesy pop songs with Fender vibrato on it to make me puke.

Then, in 1967, Jimi Hendrix told me to never listen to surf music again. I took his advice. I still have a hard time listening to Gilmore when he used it.

Along with ALL my vintage Fender amps, the Showmans, Deluxe Reverb's, etc, I removed both the vibrato and tank reverb circuits. I used the extra tube stage for more useful purposes. My amps have a tube based loop for my Lexicon reverbs. Some have different preamp designs. None have either vibrato or spring reverbs. Me happy.
I was just curious. True, everyone has their taste and their reasons. The idea of having a tube based loop for inserting effects is really appealing. Dangit Jim, now you've got me thinking, because I hardly ever use the vibrato (although when I do I like it).
"The mushroom states its own position very clearly. It says, "I require the nervous system of a mammal. Do you have one handy?" Terrence McKenna

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Post by ldg » Mon Feb 28, 2011 1:24 pm

I have a somewhat similar issue as the original poster, but maybe I'm committing a bit of a thread hijacking here.

I actually like the way my (recently purchased 69 silver face) Champ sounds when it's cranked to ten. My problem is the very small clean headroom it has. It's breaking down from about 3, and even below that it's not really clean (tested with HB pickups).

Initially I suspected the original oxford speaker, but then I tested the amp with two different cabinet and got a nearly identical behaviour.

It has a "Fender Special Design" 013341/7025 for the preamp (is it possible it's there since 1969?), then an Electro Harmonix 6V6GT (I think this one installed quite recently), and then an RCA 5Y3GT (this one is old I guess).

What do you think should be my next step?
thanks
ldg

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mattcastore: please let me know if you think I should start a new thread :)

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Post by Jim Williams » Tue Mar 01, 2011 7:56 am

Just shove a 6L6 in there and enjoy the extra volume and wattage.
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Post by ??????? » Tue Mar 01, 2011 9:36 am

might want to adjust speaker impedance, as well, if switching to 6L6. Otherwise, the loss in efficiency would work toward negating whatever small increase in power/headroom could be had.

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Post by ldg » Tue Mar 01, 2011 9:47 am

thanks Jim!
Do I need to make any adjustment to accomodate the 6L6?

Btw, I took the speaker out today and discovered a little tear (4-5 millimeters, near the edge). Also, one side of the speaker's "skeleton" is covered by heavy rust (also parts of the magnet bit). I went out and ordered a Jensen P8R, I'll let you know what difference does it make...

cheers!

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Post by Jim Williams » Wed Mar 02, 2011 9:38 am

I could have sold you my Jensen 8". It's one tinny sounding, brite as hell speaker with no low end. Worst thing that you can put in a Champ, to my ears. Mine came with one and I ripped it out ASAP. I used a Mojo tone 4 ohm Eminence and that sounds great, real smooth and balanced.

Impedance drive levels don't change that much from 6V6 to 6L6, no need to rewind the output transformer. Yes, it will put out more watts, about 10. Yes, it will be louder. Yes, it will be louder before break-up. Yes, it will drive an efficient 4x12 cab to band practice levels.

I also removed the 1k power resistor in the power supply and fitted in a Deluxe Reverb choke. That removed the residual hum so I can record with it now. I removed the can electrolytic filter cap and used a pair of dual 100 uf 500 volters, that removed the rest of the hum.

I used the vibrato tube as an extra preamp tube. It's sort of like a Marshall plexy design now. It has a master volume and a mid control. It screams and will feedback like a big amp. It's a lil' monster now.

Mine has a EH 6CA7 power tube, about 12 watts from that, I love the sound of 6CA7 power tubes as all my amps have them except the 1966 Deluxe Reverb, that has a pair of GE6550's for 80 watts output using 100 watt transformers.
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Post by ??????? » Wed Mar 02, 2011 9:52 am

Jim Williams wrote:Impedance drive levels don't change that much from 6V6 to 6L6, no need to rewind the output transformer. Yes, it will put out more watts, about 10. Yes, it will be louder.
wha?

:?

Jim, I respect your knowledge of audio electronics immensely, so I ask this question in good faith.

I'm sitting here looking at data sheets for 6V6GT and 6L6GC.

In class A S/E operation (like in a Champ), Zout of a 6V6GT is listed as 8,500 Ω with a Va of 315VDC.

In class A S/E operation, Zout of a 6L6GC is listed as 4,200 Ω with a Va of 350V. With an "apples to apples" 315V plate voltage, it seems that Zout would be even lower than that figure in a 6L6GC, no?

To me, a Zout of more than double is a significant enough change in output impedance that I'd want to adjust the speaker load accordingly, assuming the output transformer turns ratio is kept constant, if my goal was increased volume and headroom.

What's the reasoning behind saying the impedance levels "don't change that much?" Is there some hidden factor that makes this true in the champ, as opposed to on the data sheets? Because I can't find one. Bear in mind that I'm completely self-taught and whatever knowledge I have is 'practically acquired' knowledge. However, I can't make this add up. Maybe you can help.

Regarding the headroom and volume-- yes, assuming matched impedances, I agree that it would be significant... on the order of about 3dB, I think, correct? Maybe not earth-shattering, but definitely noticeable. However, if the speaker is kept stock, it will never be a world-beater in terms of volume.

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