Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dunner84 on July 02, 2015, 02:49:57 pm
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I will be starting a new build, and I really like the idea of the 1 channel Hoffman Deluxe Reverb with no trem.
I have a few questions:
Does anyone here have experience with this amp or any of the Hoffman DR amps?. I can't find any sound clips anywhere. So I am basing this build on features that I want.
I would be ordering the Iron and the Reverb tank from him; they seem to be decent quality.. Also, I plan on using big enough iron to switch between 6V6 and 6L6 power tubes.
Does anyone have experience with DR amps that have no trem circuit? I am curious to know how it would affect the gain and overall tone.
Here is a link to the Schematic I am working from.
http://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf (http://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf)
I don't have a lot of experience with these ab763 circuits. Where I live, there isn't a lot of cool old gear floating around to mess around with.
I should mention that, I like what I hear in the Allen Accomplice. From the outside, the Allen amp seems similar to the Hoffman; (1 Channel, w/Reverb and no trem) I will probably add the RaW control to the Hoffman circuit too, and use a relay so that I can set it and turn it on and off with a footswitch.
Any advice would be very helpful.
Thanks
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The schematic you linked also has tremolo. You'll need to strip that out. Hoffman's design is solid and has been proven many times.
Here's a DR that I built several years ago. Single channel, reverb, no trem, and iron that will support 6V6s or 6L6s.
http://home.comcast.net/~seluckey/amps/tdr/tdr.htm (http://home.comcast.net/~seluckey/amps/tdr/tdr.htm)
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As Steve said, my 1 channel AB763 has trem and reverb
I am just eliminating the normal channel in the one channel AB763
The image below shows the trem section that would have to be removed if you did not want trem
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Thanks for all the replies. I found some good info on another forum from someone who built one of these amps, and it left me with a few questions.
I have decided to leave the tremolo in. Aside from a few mods like the RAW control and maybe a master volume, I want a DR with the ability to replace the 6v6's with 6l6's. Does the layout provided show the proper component values to be able to do this? I don't have any experience with this circuit so sorry if these questions seem silly. It looks like the default transformer options in the price list will handle it; although, I am not sure about the other components.
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The 6L6's will pull more B+ current so a stouter power transformer will help keep voltage sag nominal.
A beefier output transformer will allow you to get more volume out of the big bottles.
An output transformer with a multi-tap secondary will allow you to match the loads required for both the 6V6 and 6L6.
You may not be able to get the tremolo to work properly with 6L6's. Most big bottle amps use signal tremolo versus your bias tremolo.
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> trem section that would have to be removed
You might also want to omit and bypass the Intensity pot? (Below)
I realize the OP has changed his mind, but someday someone might want to follow his original path.
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Thanks for the info. The Transformers in the price list look like they were meant for 6l6s. I was more worried about cap and resistor values.
It is also interesting about the tremolo possibly not working. I Don't know much about the AB763 circuit, but I was reading on the website here and Doug said he uses the same one as on the 6G16 Vibroverb which I think uses 6l6s.
Sorry for the questions, but I find it a little confusing because I don't have experience with the real deals. So all of these amps are ab763s, and the differences are transformers, tubes, and speakers (plus little things like tone controls etc.)?
The power transformer on the parts list says it's for a Super and the output is 40w with 2, 4, and 8ohm taps. I am curious if that is too much for 6v6s to work. Will a 5AR4 Rectifier tube work as well or does it need to change with the power tubes?. It is important for me to be able to switch between them relatively easily. This is my first foray into an amp with this kind of ability.
Thanks
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It is also interesting about the tremolo possibly not working.
It will work, but it may not be as intense as you like. That trem circuit modulates the bias voltage to the output tubes. 6L6s require more bias voltage than 6V6s so the signal from the trem oscillator needs to be a bit stronger to overcome the higher bias voltage. Also, there is a compromise between optimum biasing and optimum tremolo. You'll likely have to compromise. I would not worry. There are several things you can easily do to boost the trem intensity.
So all of these amps are ab763s, and the differences are transformers, tubes, and speakers (plus little things like tone controls etc.)?
That's correct. If you just look at the schematic you would think they are all identical.
The power transformer on the parts list says it's for a Super and the output is 40w with 2, 4, and 8ohm taps. I am curious if that is too much for 6v6s to work. Will a 5AR4 Rectifier tube work as well or does it need to change with the power tubes?. It is important for me to be able to switch between them relatively easily.
The 5AR4 is used on both the SR and DR. I would not want to run 6V6s on iron made for a Super Reverb. JJ 6V6s will handle the voltage but then you gotta remember about changing speaker loads when you switch between 6L6s and 6V6s. And you gotta reset the bias. And you gotta tweak the trem. Just isn't worth it IMO. And you will not hear much difference. The 6L6s will have a little stronger bottom end (my preference) but otherwise they will sound very similar. I'd just choose one or the other, get the iron for that choice, optimize the amp, and never look back. It's not gonna be as simple as pull these tubes and plug in the other tubes. However, a lot of people like to tinker with that stuff. I was one of them. For the first month after I built my DR I did all the tinkering that I read about. Ended up with 6V6s like it was designed for and been running it like that for over 10 years. 'Course I've built a lot of other different sounding amps since then so I can just plug into a different amp rather than swap tubes. There are days when one amp sounds so much better than another amp, then tomorrow it may be a different amp that sounds better. And there are those days that none of them sound good! I don't play long on those days. :icon_biggrin:
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There are days when one amp sounds so much better than another amp, then tomorrow it may be a different amp that sounds better. And there are those days that none of them sound good! I don't play long on those days. :icon_biggrin:
:laugh:
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Thanks again everyone.
The reasoning for want/need for tube swapping is more of a headroom issue than anything. I am stuck in a weird place where I want to use it in my house, but it also needs to be giggable. Maybe a really good master volume is the way to go; however, I am not a fan of them. Are there any good ideas for some kind of half power mode for this circuit? At the end of the day, if I have to choose one and stick with it, I will. I just want to explore all my options, and gain as much versatility as I can. My wife only has so much patience for the amount of space I take up with my gear. Between the Marshalls, the Tweeds, and the old oddball stuff, I don't think I could squeeze in two blackface amps.. 1 is already pushing it :)
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Hi JGK
I知 in the process of building a AB763 Deluxe Reverb myself I知 using a mix of ideas since I am stuffing it into a Princeton Chassis. Right now I am trouble shooting since I rearranged allot on the circuit board and used a post PH master volume I am in fact getting ready to post some info since I知 having problems in a few areas. With thoughts on a the AB763 format building to do 6v6s and 6l6s I値l just add my 2 cents. I have built a Allen Accomplice great amp I can run 6v6s in it but the PT is pretty stout and I値l use a 5y3 rectifier in it to keep votages low enough for NOS 6v6s, J and Js will handle extremely high voltages but I don稚 really like the sound when pushed hard just my opinion we all hear sound differently. I keep my Accomplice set up with the best GE6l6s I have and bias them a bit hot great amp think Fender Vibroluxe with out vibrato. I guess my point would be between output impedance mismatches and fine tuning its probably wiser to spec out an amp out for a primary set of tubes. I have a Vibro Champ clone I built that is set up to accommodate either 6l6s or 6v6s with switchable cathode bias and impedance matching but I only run 6v6s in it I find 6l6 have a bit more clean headroom but also sound a bit stiff if that makes any sense. All good sales crap but you find when trying to accommodate too much you compromise something else. Find a good pedal for the house stuff. Just my thoughts good luck with you build since amp building is terribly addictive. JGK