Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Tyrannocaster on June 14, 2012, 07:05:03 am
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I'm working on my 5E5 Pro build and last night as I was looking at the schematic it occurred to me to wonder why you couldn't put in a switch to bypass V2A. Here's a schem that shows the two preamp tubes on this series of amps:
(http://i425.photobucket.com/albums/pp332/Tyrannocaster/RATweedProLuxe3.jpg)
(Just disregard the red changes, etc. The relevant part is accurate. And I realize that I screwed up which side of the first tube gets the tone control, LOL. I just haven't updated the schematic. This mod would also necessitate a different trem circuit, I guess one of the power tube bias circuits - probably the early Tremolux)
Now, I have an old '55 Tweed Deluxe but it is a 5D3 - totally different setup. But I've played 5E3s and I do know that the most common complaint with them is the lack of headroom. My 5D3 has good low volume clean tones, but the phrase "low volume" is the key - it gets dirty pretty fast, too. Is there a reason why this mod never seems to pop up in discussions of the 5E series? I have a Weber DPTDT relay just sitting here that I could use to do the switching and there is a nice little hole in the chassis already, just waiting for something to occupy it. :) Seems like it would give you an entirely different amp with the flip of the switch.
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V2A is needed to amplify the signal enough to drive the 6L6s to a reasonable power level.
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An alternative consideration. You might be able to use the switching on a 5E3 with 6V6's, but I personally would not do it that way. I'd rather switch something that gives it a clearer tone without a gain/volume drop.
You can easily parallel (or use series) with resistors and/or caps to change the tone & headroom.
With respect, Tubenit
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Well, you guys probably know best. But I'm going to try it (without the switch) once the amp is together just to see what happens with just the single stage. So the PI in the 5E series must require a lot more input than the 5D series, I guess.
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So the PI in the 5E series must require a lot more input than the 5D series, I guess.
Yes.
The 5D3 uses a paraphase inverter. Each triode in V2 is actually part of the PI. And each triode provides gain.
The 5E5 uses a split load PI that consists of only one triode in V2. This type PI has a gain of only 1 and that is not enough to drive the output tubes. V2A is an amplifier stage just prior to the PI and it provides the gain needed to drive the output tubes. Many people consider the V2A amp to be a necessary part of the PI. I just think of it as a gain stage. The net results are the same.
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This type PI has a gain of only 1 and that is not enough to drive the output tubes.
No, I guess a gain of 1 wouldn't quite be enough. :laugh: I didn't realize it was so low; Thanks.
Tubenit, thanks for the schematic of the "more headroom" version. Coupling caps, coupling caps, coupling caps. I always seem to end up using lower values than stock Fender so your idea fits right in with what I like.
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I'm your huckleberry.
Through 5Ex, the PI were paraphase
Wrong! The Tremolux 5E9 is the only 5Ex amp with a paraphase inverter. At least 7 others, including the very popular 5E3 are not paraphase inverters.
The 5Fx tended to be cathodyne
Well, what about the famous 5F6A? Or the 5F8? Neither are cathodynes. I'm not even gonna look for more.
Maybe you're confused about the names of the different phase inverters?
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How about (dare I mention it) adding feedback around the PI/output stage to reduce the gain a few dB?
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Not a bad idea, really. If it's switchable. The best known Bassman used that - any Fender amp with a Presence control uses a NFB loop. In general, I prefer the raw sound of no loop, but here, I was looking for something a bit tamer and that might be a good idea if it's on a swich. Thanks for mentioning it; I'd conditioned myself to think of NFB as a four letter word for the 5Dx and 5Ex series (although the Pro 5E5A used it - which is one reason why I'm building a 5E5nonA, LOL).
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I did a review of the common fender schematics and came to the following conclusions...
There's an easier way to do this.
Dave Funk's Tube Amp Workbook runs down Fender amp models. I don't know if the original intent was that the "5" in "5F6A" would stand for "50's" but it's convenient now to think of it that way.
Skip to the final number in the model designation. The is the amp #; the Champ is #1, the Princeton is #2, the Deluxe is #3, etc. The numbers were assigned in the probable order they were developed.
The middle letter is the revision. So a 5C3 Deluxe is an earlier variant that the 5E3 Deluxe.
Catches:
- You'll almost never see a schematic for a "5A-" anything, at least not in original form from Fender. My guess is the model designation system wasn't created until after the "A" versions had been superseded, especially since some of those amps were originally made in the late-40's (and generally with different names/model designations).
- Some models were introduced at a time when other amps were in their D or E revisions. As such, those models were typically first designated with an "E" (or whatever) even though it was the first version. An example is the 5E5 Tremolux. I owned a '55 Tremolux, the first year they were introduced (production #45), and it was designated a "5E5". Interesting sidenote, you'll never see an original schematic for a 5E5, because soon after, the 5E5-A revision was released. The only change was moving the trem on switch from the Depth pot (where it made some sense) to the Speed pot.
At the start of the 60's, models were revised and all began with "6G-" even those who never went through an F variant (like the 5E3 being revised to the 6G3).
Throughout the 50's, there were a lot more variations between models. So it's easiest to follow changes to a single model. That's because depending on the amp, you can generally find differences between different "D" or "E" variants (some small, some large). Things somewhat converged during the early 60's, but when the blackface amps were released, Fender pretty much evolved to 1 standard circuit, with exceptions for special application. These amps largely varied in the size/number of output tubes and size/number of speakers. A side benefit to the convergence, from a marketing perspective, is that the entire line essentially had "the Fender sound".
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If you're looking for more 'headroom' in the schematic at the start of this thread, how about replacing the driver/cathodyne altogether with a LTP? (You could even go to fixed bias as well)
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Keep me honest Sluckey
I'm your huckleberry. Stick around.
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5e9a, FP, 5g9 LT
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Interesting. The 5G9 Tremolux is the only "5G"-anything amp I can find. But I also can't find a 5F9 schematic. Regardless, it switches to long-tail when every other Fender amp switches to long-tail and fixed bias, except the Champ.
Is the presence and NFB better as part of the PI circuit or as an extension of the Tone Stack (See 5F6 and 5F6a schematics ?
Try and see what you think.
I haven't tried both ways. I do however note every other amp in the world generally copied the 5F6A, with the phase inverter stacked on top of the feedback return.
You're probably less likely to turn your amp into an oscillator if you bring the feedback loop to the PI, rather than farther back in the circuit.
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Interesting. The 5G9 Tremolux is the only "5G"-anything amp I can find. But I also can't find a 5F9 schematic. Regardless, it switches to long-tail when every other Fender amp switches to long-tail and fixed bias, except the Champ.
AFAICT the 5G9 was one of the earliest with a LTP inverter - debut in 1957 (along with the 5F6)
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The 5G9 Tremolux is the only "5G"-anything amp I can find.
Here's one more. Has that funky trem...
http://www.el34world.com/charts/Schematics/files/fender/VIBRASONIC_5G13.pdf (http://www.el34world.com/charts/Schematics/files/fender/VIBRASONIC_5G13.pdf)
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If you're looking for more 'headroom' in the schematic at the start of this thread, how about replacing the driver/cathodyne altogether with a LTP? (You could even go to fixed bias as well)
Since this is very similar to a 5E3 preamp and we are talking about more 'headroom', I'll ask the same question that I asked elsewhere today:
-Has anyone seen on a scope (or know by other observations) which breaks up first in a 5E3, the driver before the cathodyne or the power tubes? (Seems like it wouldn't be the input preamp or cathodyne???)
Without knowing this I'm not sure how to get a "more headroom option" in a 5E3 that I'm about to build.
Thanks
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The 5G9 Tremolux is the only "5G"-anything amp I can find.
Here's one more. Has that funky trem...
Interesting. The Vibrasonic apparently debuted when the 5G12 Concert did, in 1959, both with brown tolex.
I suppose these are the exceptions that prove the rule. :icon_biggrin: