small single-ended amp with headroom

[J M Fahey]

If you have experience or have heard of a little unit that doesn't turn to dirt on 1, I'd love to hear about it.

Start by "hearing" posts #6 and #11.
Other valid options were mentioned, but for starters you just can't go wrong with a classic simple 5W amp and a good speaker.

[catnine]

Well to explain it further. The wall voltage here is 117 to max 119VAC so at 119 VAC my B+ is 390VDC and the plate 387 VDC, this is on the homebrew champ. The 73 champ I had did have a higher plate at around 410VDC and B+ 418 but that was after I biased the 6V6 at 14 watts. With the stock cathode resister of 505ohm the plate was 374 VAC and B+ was 385 VDC but this is because of my line voltage at 117 VAC . Now if you have a line of 125VAC like many do these days it all goes up.

To explain the 2 twelves . when I got the 73 SF champ which is the only Champ I ever ran through 2 twelves was bought off Ebay and came with some high gain Torres mode so with the stock speaker all it did was breakup . I them plugged it into a 2 twelve cab I built and right away it had much less breakup and that related to cleaner and louder since it was pushing more air . Since the seller gave me all the old parts I took out the torres mod and reinstalled all the original parts and through the stock fender speaker it was of coarse cleaner and through the 2 twelves it was also louder and cleaner still and had much more bottom end because of the twelves.

Once I recaped the champ and re-biased it to run the 6V6 at max 14 watts it was cleaner and had about the same bottom end . Then I got a weber sig8S alnico and the 73 champ didn't flub out on bass notes and broke up less than with the stock champ speaker.

The champ homebrew I built after I sold the 73 champ has a jensen C10R and is still running off the same 119 VAC and when I built it I made certain the 6V6 was running close to 14 watts and used a JJ 6V6s and JJ 12AX7 and NOS 5Y3 the B+ is a bit lower than the 73 champ at 390 VDC and the plate around 385 VDC both biased at 14 watts . All I know is a SF champs PT is 275-0-275 @70 mA and the weber PT is 330-0-330 at 100 mA but then the weber OT even though the same size as the SF champs as is the PT the weber OT could cause the voltage drop at the plate they are not the exact same OT's weber did say they are exact copies but who knows. I did build the homebrew using all the same componant values off the fender schematic yet it comes to tranny's who know's where the difference is. The Weber PT did come with a 120 and 125 Volt line tap so I used the 125 so that did cut it down some on the line end, with the 120 my heaters were a bit over 6.3 volt . It alos came with two sets of HT secondaries 300-0-300 and 330-0-330 I usd the 330 because it was closer to a SF champ and I wanted the amp to be clean as I could get it.

[Chuck H]

I didn't know the stock Champ speakers broke up like that. I've never played a Champ with a stock speaker. Now I know why

[deci belle]

Check out the Fender Model 80 schematic, from the 50s. It was designed for use with the "White" Hawaiian Steel guitars.

It didn't want to break up like it's design-sibling, the Fender tweed Princeton. I didn't know about pedals in those days… (early 70s)

http://www.el34world.com/charts/Sche...te_model80.pdf

[catnine]

Check out the Fender Model 80 schematic, from the 50s. It was designed for use with the "White" Hawaiian Steel guitars.

It didn't want to break up like it's design-sibling, the Fender tweed Princeton. I didn't know about pedals in those days… (early 70s)

http://www.el34world.com/charts/Sche...te_model80.pdf

Interesting , you had one of these amps? It's a lot like the 5F2A except the tone and vol are wired differently . the pots wipers both come off the grid of the 12ax7 where the 5F2A the wiper of the vol pot connects to the grid and the tone wiper come off the 12ax7 preamp plate and also through the 1 meg vol resistence path to ground . I'll need to study that a bit to see how they interreact.

[deci belle]

Yeah, it wouldn't break up. I had a Morley vol/wah pedal and on max wah, I'd get it to sizzle a bit, with an SG. I had the Hawaiian guitar too, on its three legs.

[leadfootdriver]

Try this one out. It's pretty loud if you ask me. The Vox schematic that I lifted the 4th stage from has a 4.7k on the cathode, but I didn't have one. But I did have a 3.9k! I have a 1.5k grid stopper on the EL84.

[catnine]

I was thinking about this topic and I agree that to have a clean /more headroom SE amp that a 6L6 and larger OT would help . When we talk about gain and point of breakup verses watts I look at the early fender champs and then the BF and SF champs all that used a 12ax7 and a 6V6 . I realize the early tween champs had a lower power PT. and on top of this they had higher value node resisters further dropping the voltage and lower value filter caps and more NFB , yet they had no tone pot to drop the gain . Later BF champs had a higher voltage PT lower value node resisters higher value filter caps so they used a higher voltage and used bypass caps on both triodes and less NFB and had a BF tone stack that created a loss in gain to the second stage was increased to bring the loss back. Where the tweed champs maybe used one bypass cap in the preamp or none , BF champs used them across both stages . All had a 8 " speakers and all were disigned to be practice amps .

Yet I have read fender never expected people to crank them up mostly the tweeds. I think the BF and SF champs were designed for more volume and headroom since fender later realized that people wanted a bit more loud possibly due to they wanted to play in a garage band with a drummer and couldn't afford the upgrade to a P-P amp.

You need gain to get power yet what is the line between gain and breakup?

[riz]

I have an old BF Vibro-Champ. I put a good speaker in it, and chose the sweetest sounding tubes in my stash (including a lower gain 5751 for V1), and I plug into Input #2, which is of course attenuated. It is so warm and clean and huge sounding, and you can use the volume knob all the way up and it still stays together. If I want more, I just plug into Input #1, but I never seem to do that any more. With a good speaker in the mix, the actual watts really become just numbers... This amp is more than enough for home or shop.

What I'm trying to say is, I guess, that this circuit topography exists right under our noses, but few of us take advantage of it. I didn't for years. There is a whole 'nother amp just sitting there inside that circuit!

[catnine]

I have an old BF Vibro-Champ. I put a good speaker in it, and chose the sweetest sounding tubes in my stash (including a lower gain 5751 for V1), and I plug into Input #2, which is of course attenuated. It is so warm and clean and huge sounding, and you can use the volume knob all the way up and it still stays together. If I want more, I just plug into Input #1, but I never seem to do that any more. With a good speaker in the mix, the actual watts really become just numbers... This amp is more than enough for home or shop.

What I'm trying to say is, I guess, that this circuit topography exists right under our noses, but few of us take advantage of it. I didn't for years. There is a whole 'nother amp just sitting there inside that circuit!

I had a 73 SF champ no Vibro and all I did to it was do a recap job and got a weber sig8s alnico speaker and it sounded real good . The champ I have now is the exact same circuit and the same type resisters and all other componant values in a narrow panel tweed style chassis that Allen Amps used to sell so it has the three holes to make the same tone stack and the same tubes I even used a 40uf for the first filter cap because the 73 Champ I had had the orig cap can 40/20/20 and I replaced it with the same .

The cab is a bit larger one I made myself out of mahogany plywood and I have a ten in it. I built this cab for a few amps and kept it and altered it to fit this chassis since I already had it. What 8 inch speaker did you use? I did think about using a 5751 in V1 but never have . I use strats I built but they are all vintage type single coils , never tried input #2 . I will try that and the 5751 .

[deci belle]

The only difference in the signal paths shared by the nearly identical Fender Model 80 (White) and the 5F2a (Princeton), as far as I can tell, is that the 500pF tone cap is before the tone and volume pots in the White, and between the tone and volume pots in the Princeton— everthing else boils down to the same circuit, by my method of deduction.

I didn't check the 5F2 schematic for comparison to the White.

I see the main difference is in the power sections, though. There are no voltages indicated, but there is only one 16uF/450v cap between the 5Y3 and the OT on the White, whereas the 5F2a has two: the main reservoir and another feeding the OT.

Both have an 8uF/450 at the screen, and another feeding the AX7 plates.

Other than the Princeton's beefier filtration at the start of the B+ rail, the only other difference I see is the grid leak resistor at the 6v6's input. The weird thing is that the White has the higher value (270k). The Princeton has a 220k there. I thought a lower grid-leak resistor value results in less gain (that would be the Princeton)!

So I don't know why my White wouldn't break up, after all. I know it had an AX7 cuz I replaced the original one once from my dad's Collins tube stash. If it had acquired a 6k6 sometime before that might explain it, but I'll never know.

Maybe the White had higher voltages(?) its schematic does specify higher voltage caps in some places (600 as opposed to 400) hmmmm~ other than that, it was an extra cheaper student amp combo with a Hawaiian guitar sold door-to-door in Santa Ana and Fullerton, Ca.

It was always so frustrating back in those days (early 70s) that it didn't break up at all cuz my hero was Neil Young. haha!!

[PeanutNore]

The Champ-copy output stage in the VHT Special 6 works great with a 6L6GC if you use a 270r cathode resistor and 4k5 primary on the OT. Some folks on this forum (including myself) have modded theirs like this. Others have measured the output at 11+ watts, my experience is that you can get a pretty damn loud clean tone at 12:00 on the volume knob with a decent speaker (I use a 1x15 with a Delta 15a, ~100dB 1w/1m).

[Chuck H]

I said above, and I'll stick to it, good clean tone is at least partly dependent on having some watts you don't need. But we shouldn't let the thread devolve into a "How to make a Champ louder" tutorial. It's one thing to want a tight tone at Champ power levels. In that case it makes sense to tighten up the amp and maximize efficiency. If the goal is actually more power a Champ is just the wrong amp to begin with and the effort is, IMHO, counter productive to the whole point behind single tube, single ended amps for guitar. First we wanted smaller amps so that we didn't need to blow our heads off to get cranked tone. Now we have the smaller amps and we want to make them louder.?.

[teemuk]

First we wanted smaller amps so that we didn't need to blow our heads off to get cranked tone. Now we have the smaller amps and we want to make them louder.?.

Guitarists have never had problems in being illogical.

In many ways we've gone through a full circle with this. We were marketed the concepts of attenuators, dummy loads or power scalers, then inexpensive , low power pract... cough... "studio recording" amps. Then reamps to amplify them to higher output levels. Newest Fryette product is a tube reamp, obviously so that one can reamp his low power cranked amp while getting power tube distortion from the reamp.

I obviously don't have to understand everything but the markets seem terribly excited about such product right now. ...As it always does for everything new. I think its called "trends" or something, wouldn't worry about them too much in the long run of things.

[Chuck H]

We were marketed the concepts of attenuators, dummy loads or power scalers, then inexpensive , low power pract... cough... "studio recording" amps. Then reamps to amplify them to higher output levels. Newest Fryette product is a tube reamp, obviously so that one can reamp his low power cranked amp while getting power tube distortion from the reamp.

New product idea... A 250W SS power amp with an input capable of providing a proper load to a tube power amp and padding it for reamp. That's not the new idea, obviously. It's the Ho or Ultimate attenuator (the one that the Fryette Power Station reports to have improved upon). The new idea is to make the input sensitivity such that it can be used to make a little amp a big amp and then build it into a 2x12 Celestion loaded cabinet (since little amps don't have big speakers). Got a little tube amp and love the tone? Want that tone loud enough for stage use? Buy this item NOW!!! Don't ne fooled by imitators.