Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: harryk on June 25, 2010, 04:52:54 am
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:smiley: I have a nice tweed combo cab for one 15" speaker made by Mojotone. It was planned for a Fender Pro 5E5-A amp, but I am now thinking to do something else of it. It came to my mind that I would like to try following combination: Fender Bassman 5F6-A preamp + one (12AX7) Tubenit tube reverb + Deluxe 5E3 PI + power amp with 2x6V6GT tubes. I am not in a need of huge power and I like very much 6V6GT sound. Has anybody created such a combination? I try to achieve legendary 5F6-A sound with lower sound pressure and added with reverb. One thing which worries me is how 5E3 PI without preceeding 12AX7 stage works with 5F6-A preamp. Harry
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I probably would not do that combination myself if you're hoping for a 5F6-A tone? I think the 5E3 PI & power amp would signficantly change the tone. If you're wanting a lower power version of the 5F6-A tone just build one with reverb and use 6V6's. Take a look at the Texas Raptor.
The Raptor has some of the 5F6-A topology with a paralleled triode in V1 & cathode biasing. Using the SCH schematic you can change the component values to match a 5F6-A and if you like use a spst to switch a V1 into being single or paralleled triode.
http://www.el34world.com/Forum/index.php?topic=2442.0
With respect, Tubenit
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My main amp is a 5F6a with a BF Deluxe PI and power amp with SF Deluxe (higher) voltage to the PI and power amp for more headroom. It's a great amp and it easily hangs with 45 watt Fenders without even pushing. Voicing beats wattage every time for cutting through the mix.
I like what you have in mind. It may not work out exactly like you expect (these things rarely do) but I'm betting it'll sound great if done correctly. These accidental surprises can turn out to be the best amps... so try it. It'll almost certainly turn out to be someone's perfect amp. Hey, I built a small 15 watt mofified Deluxe for warm, clean Motown chord work. it was perfect; I used it for that for 3 years. I never figured anyone else would want one. I loaned it to a player that cranked it up for full gain and suddenly I have 2 orders and a lot of possibles. It had never occurred to me to try playing it like that.
I love accidents!! :grin:
Go for it!
Dave
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These accidental surprises can turn out to be the best amps... so try it. It'll almost certainly turn out to be someone's perfect amp.
I second that emotion....sounds like it will be great.......try it!
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I once did this exact same combination (Gain > Gain > CF > TS > Reverb > Paraphase > 2x6V6s)
The results were very disappointing, the amp was weak. A 5E3 sounds the way it sounds because the preamp is pretty straight, simple and lossless. If you wanna put a tone stack there, and keep the paraphase, add a gain stage before it (ala 5E7). Or use a LTP.
My 2 cents...
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I once did this exact same combination (Gain > Gain > CF > TS > Reverb > Paraphase > 2x6V6s)
The results were very disappointing, the amp was weak. A 5E3 sounds the way it sounds because the preamp is pretty straight, simple and lossless. If you wanna put a tone stack there, and keep the paraphase, add a gain stage before it (ala 5E7). Or use a LTP.
My 2 cents...
:rolleyes: That is the question which I had in my mind. I would like to keep 5E3 character and touch response but add something of 5F6-A to it. I am not very willing to add one more stage to planned configuration. More stages, more compression and less head room + dynamics which I am seeking in this case. Harry
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I've actually tried almost exactly the combination you're planning, here are my notes:
- The bassman front with the cathode follower has excess gain for the cathodyne PI and cathode-bias 6V6:s.
- The bassman tone-stack has lots of bass and scooped mids which makes the 6V6:s fart pretty badly
I eventually tweaked the tone-stack for less bass and more mids but the overdrive I get is still kinda harsh. I guess different PI, maybe paraphase or LTPI might change this but I haven't had time to mess with it.
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Cool idea and I am always surprised that this type of amp is not discussed more.
However, I don't think the 5E3 PI is the way to go as there is hardly any drive before the PI in the 5E3 so the magic happens in the PI and beyond.
You could try a Blackface Deluxe front end onto a 5E3 PI and PA just like the %13 CJ11.
Alternatively I think a 5F6A front end & PI with a 22K tail and a 5E3 PA would be a great amp. I recently converted my 5E3 into a AB763 front end, 5F6A PI with 22k tail, 33k/68K split load before the PI to loose some gain, no NFB and a 5E3 PA. It still retains a lot of the Tweed and 5E3 character yet is IMO a more versatile amp.
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:smiley: Thanks guys of good ideas. It always helps when somebody else is also thinking these things. I like Deluxe Reverb clean sound very much, but when it distorts, it is not the best sound to my ear. I think that it has something to do with DR tonestack and bass response. Still the key idea is find a pretty simple configuration where amp breaks to distortion nicely without too much gain and responses to playing touch very well. I have to continue thinking of your ideas. Harry
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I once did this exact same combination (Gain > Gain > CF > TS > Reverb > Paraphase > 2x6V6s)
The results were very disappointing, the amp was weak. A 5E3 sounds the way it sounds because the preamp is pretty straight, simple and lossless. If you wanna put a tone stack there, and keep the paraphase, add a gain stage before it (ala 5E7). Or use a LTP.
My 2 cents...
I said "paraphase" but was thinking "cathodyne".
It was not a bad amp really, but nowhere near as good as a real 5E3, nor a real 5F6A. It was lacking "omph", and was barely crunching.
Look at the old schematics. When Leo wanted a split load PI and a cathode follower + tone stack, he put a gain stage before the PI (5E7 / 5E5A / 5F4).
I ended up converting the amp to a 5F6A preamp and PI, feeding a 5E3 style 6V6s cathode biased power amp and 12" Alnico, and that was a good one.
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When Leo wanted a split load PI ... he put a gain stage before the PI
Everyone puts that gain stage in front of a split-load, all the time.
Because there is no gain with the split-load, the input voltage has to be as big as the voltage needed to drive the output tubes. So the "pre gain" stage ahead of the split-load takes a typical signal fed to a power amp and boosts it to drive the inverter and then the output tubes.
Notice in Fender amps that use a split-load and have feedback, the feedback loop is always returned to the triode ahead of the inverter. For most guitar amps, I tend to think of the area enlcosed in the feedback loop as the power section. Regardless, it is usually best to consider that triode before the split-load as an integral part of the inverter.
So if you didn't have one between your reverb and the split-load in the amp you built, you might have had a lack of oomph because the preamp didn't deliver enough output to directly drive the output tubes, and the stage that would make up the difference was missing.
When describing phase inverters, writers rarely point out that the stage ahead of the split-load is what will allow something closer to apples-to-apples comparisons with other inverter circuits.
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So if you didn't have one between your reverb and the split-load in the amp you built, you might have had a lack of oomph because the preamp didn't deliver enough output to directly drive the output tubes, and the stage that would make up the difference was missing.
Thanks for the great explanation HBP. You've nailed it, a cathodyne really needs a gain stage right before it to work properly, and that's not what happened in my build, and not what would happen in the amp Harry is planning to build (the cathodyne would have the reverb circuit + a tone stack + a cathode follower, and then only a GS before it).
I would advise against building it like this.
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I agree with you.
Start your count this way: output tube(s) + 1 preamp tube (2 triodes). That's your power stage, regardless of what phase inverter you use. The selection of which circuit is just the details, and how many supporting components you need.
Whatever you have aside for the output tube(s) and dual-triode bottle, that's what you have to work with for preamp and effects.