The Workbench

Best Reverb in a tube amp you heard in your life so far.

26

"Never could have dreamed that option exists! You have photos ?"

Links here to sources here.

https://www.google.com/sear...

I'm pretty sure that Bruce Zinky mentioned on several occasions 30 years ago that he preferred the Dual Pro to the VK but some of us go for the spaciousness of the 3 x 10" speaker combination.

27

after leaving fender, zinky started his own company...i remember he had a purple velvet covered amp!....he also owned the supro name..before selling it to the guys that kickstarted the brand on long island ny...just recently resold to d'angelico guitars!

for me a perfect vibro king would have 15" speaker ....replaced baffle

here's good namm history feature w zinky

https://www.namm.org/librar...

cheers

28
– Billy Zoom

Is that for sale Mr. Zoom? If not, how do I get my name on the list?

29

yeah bz's little kahuna ...worked out the pitfalls of the original outboard reverbs + added "electric prunes" choppy trem!

he also had that great little gretsch amp that never went into production..too bad!!!

a tech legend..besides x guitar!

cheers

30

Yavapai writes:
Links here to sources here. https://www.google.com/sear...

Since you mentioned CS I thought it is going to be obscure. My apology for not trying to google images first. Clearly by the images of the rear, there is the 6V6 driver so you are absolutely right. I have to try one when it comes around.

Found one video that demonstrates the Reverb and Tremolo reasonably well.
Link

One hell of an amp. I dont mind the 100W. I can mod uninvasively to go down pretty low and have best of both worlds. It really is a Twin on Steroids.

So.. I am basically trying to reinvent the wheel and convert the test amp into a VibroKing / CS DualProfessional. Will be interesting when it is finished as I have a lot of other great unique ideas to try. Some of the Ampeg tone control circuits are absolutely fabulous, so I probably will implement that.

Either VibroKing or CsDualProfessional is definitely in my future. I think they add something else to my other favorites, 50s Tweed Deluxe and Pro Reverb.

To me Dwell is so important and it is a pity it was not standard in all other Fender Reverb Amps. When an amp is designed without Dwell, then production variations and tank and component variances can really make reverb sound pleasant or unpleasant between two identical new amps of the same model. Reason is, the Dwell must be hard set at some level, and that level is not always what the specific amp needs and is sometimes out of the sweet spot. Dwell fixes a lot of the dead/dull Reverb issues of some fixed dwell designs. Dwell is a huge benefit if you switch between archtops singlecoils and humbucker guitars playing with Dwell and Tone. That is what I find useful, but you may experience different.

Thanks to all for the kind help and info. I got all the info I need.

31

If I really knew my stuff and was going for the perfect combo, it would definitely have 3-knob reverb and I would be looking very closely at the mid-'70s silverface outboard reverb circuit. That's a lotta extra knobs and tubes, though!

32

A 1990s Ampeg Jet. And I only came up with that after racking my brain for a good while. My first amps were a blonde Bandmaster and tweed Bassman RI, and it's been all Voxes ever since other than a brown Vibrasonic and a handful of tweed or Marshall homebrews. I bought that Ampeg when I was in college as my apartment amp and kept it for a few years. That's the only amp I've ever owned with onboard reverb. But it was excellent reverb, so still a fair answer. I'm sure it was based on the Fender blackface reverb anyway, which has always been my ideal of great reverb (not ever having owned one, but having played through them many times anyway). The one time I got an outboard Fender tank, I was very disappointed. I was expecting it to sound like the onboard Fender reverb. Everything about it that surf guys probably love I didn't like at all.

33

Afire, and others,

Anyone compared a Blonde Twin with Ampegs and blackface twins. I ask because I never heard a Blonde Twin in person or played one personally. The Blonde Twins differ from Twin Reverbs in that they have Baxandall tone circuits. Twin Reverb tone controls are more simple and have a midrange hole that people got used to and now call scoop and got a lot of creative use out of. (Not as big a technical issue as the Vox Bass Hump though) The hint to my reason asking this question is that since many Ampeg amps use tone circuits close to Baxandall and therefore maybe will recognize the similarity between ampegs and the Blonde Twin. So if anyone has both a Fender Blonde Twin circa 61 and an ampeg with Baxandall Tone circuit or otherwise can remember the differences between Blackface Twin Reverbs and the Blonde Twin it would be really great to have your opinion about the tone control differences and tone differences heard.

Baxandall tone can be great if implemented correctly. One of the best amps I ever played is a Jim Kelly that was Baxandall. I still have the amp case and Cover of the head, but have no clue what happened to the chassis. It was long ago I had that amp up and running. it must be somewhere around here. It had socket issues so i must have removed it and forgot about it.

In my opinion, the Blonde Twin should sound much more "Ampeg" or "Kelly".

I found a somewhat good comparison, same speakers used and to my ears I can clearly hear the Baxandall midrange of the Twin compared to the more midrange free sound of the twin reverb. To my ears always, Baxandall gives you more of a "tongue" feel to the sound due to imo better handling of midrange.

Link

Bit difficult to figure which amp is played visually, although I can identify them by ear, but it gets clear when tremolo is used and I can then figure out the start. Crazy how little diligence people have making videos. He could just have said left right etc when he switched.

35

I want to see you tour with a full size plate reverb. Might make a great spectacle.

36

I remember the day I got my Twin Reverb after using a Peavey Classic 30 for years. We set the two up in stereo with what I thought were pretty balanced settings...the Twin's reverb splash covered up any evidence the Peavey existed. Over the years I owned it I tried out both the Black panel and Silver panel reverb circuits in that Twin. Both were wonderful, but I think I like the darker Silver reverb a little better.

I've since sold off the Twin as my living situation became too small for it, but now I quite happily get along with a nice mid-60s Ampeg Gemini I. And what a reverb! Not quite as sparkle-splash as the Fender, but very present, and all-encompassing (I believe Proteus once called it "fulminant"). Indeed, I think when you turn it up past halfway there must be electrons exploding inside there.

37

Is that for sale Mr. Zoom? If not, how do I get my name on the list?

– Sourpuss

There's one for sale in Vancouver, BC.

[Which mind as well be Mars.]

38

Hi Otter:
I guess you refer to the Gemini G12 MK I.

If so, I can see why that amp can sound nice. True to Ampeg, great input channels with Baxandall Tone controls and it doesnt look like they tried to skimp anywhere. The Reverb section looks pretty standard, but you say it sounds spectacular. Just for my sake, can you describe any plusses and minusses you hear between reverb on the Ampeg compared with what you remembered with the twin (head canceling one speaker in the twin of course)

The single tube Tremolo is a very simple circuit, and the only place they seemingly cut a corner, but what does it sound like ? Tremolo action by interrupting the signal to the tone-control of the first channel is used. I prefer phase-inverter and bias tremolo, but there is no guarantee any implementation will sound better than yours.

What does the afterbeat switch do if it is on your MK1 ?

Here is a schematic for your MKI for reference, if it is the same Amp we are talking about. But there is only one Gemini MK1 with the earliest version without reverb or tremolo I think I can remember. MK1

39

Gee Daniel, that is a beautiful amp. Looks like new !

I went and looked at the reverb rocket schematics and it seems that the tank is driven transformerless with capacitive coupling rather than inductive. In that case they would use high input impedance reverb tanks. They seem to call a reverb tank an echo-unit on the schematic.

Capacitive coupling is going to sound different. I would really like to hear that amp in person. But, what is the chance !?

– retnev

The picture of the Dirty Girl was when it was new, though it's still in very good condition as I don't gig with it much. I mostly gig with a hand-wired Princeton Reverb clone that Winnie Thomas built and sold me last year. The reverb on the Princeton is very nice too!

40

Hi Otter:
I guess you refer to the Gemini G12 MK I.

If so, I can see why that amp can sound nice. True to Ampeg, great input channels with Baxandall Tone controls and it doesnt look like they tried to skimp anywhere. The Reverb section looks pretty standard, but you say it sounds spectacular. Just for my sake, can you describe any plusses and minusses you hear between reverb on the Ampeg compared with what you remembered with the twin (head canceling one speaker in the twin of course)

The single tube Tremolo is a very simple circuit, and the only place they seemingly cut a corner, but what does it sound like ? Tremolo action by interrupting the signal to the tone-control of the first channel is used. I prefer phase-inverter and bias tremolo, but there is no guarantee any implementation will sound better than yours.

What does the afterbeat switch do if it is on your MK1 ?

Here is a schematic for your MKI for reference, if it is the same Amp we are talking about. But there is only one Gemini MK1 with the earliest version without reverb or tremolo I think I can remember. MK1

– retnev

Hi retnev, I spent some time chasing down a weak tremolo in my amp when I bought it a couple years ago, until I noticed the 1M resistor on the schematic in parallel with the trem lamp. This was absent in my amp, but when I added it the tremolo came alive. It's a typical opto-trem sound, which I've found I like better than the bias-trem. Nails the Creedence Bayou sound. The after beat switch is a neat effect, much like the Vox Repeat Percussion if you're familiar with that. I don't have a ton of use for it, and it comes with a noticeable volume reduction. It also has a severe ticking, which I still need to poke around to find.

The reverb is not as bright as a Fender, less brash and in your way. You don't have to fight to stay ahead of it, and it just fills the room behind you. If you turn it up much past halfway, it will self oscillate.

The preamp, with its high plate loads, unbypassed cathodes, and Baxandall EQ is very rich and easy to work with. It responds very well to boost pedals and my Echoplex preamp. They make quite the pair. The 7591 output section also seems to hit the magic sweet spot in between 6V6 and 6L6.

It's got a couple other weird tricks that probably contribute to its unique sound, like the cap-coupled (transformerless) reverb input and the pentode-driven concertina inverter.

Thanks for asking, it's been a while since I thought about this circuit.

41

I'm partial to the single valve Swart reverb - which is adapted from a Gibson design I believe.

42

Otter;

1) Does the ticking become less ... or less treble when you engage the after beat switch to on ?

2) Does the ticking disappear or become less pronounced if you remove the Reverb drive tube (V6 6CG7) ?

3) Or disappears when you disengage reverb ?

4) Just want to make sure; Does it self oscillate when you turn the "Dimension" control up ?

The schematic I posted (click here ) seems to be for your amp, but it doesnt have a 1M resistor across the lamp so maybe my questions above would not be valid as the circuits used may be different. Shuggie;

The Swart Tweed Amplifiers are probably among the best tweeds out there. I yet have to hear a bad sounding video. I can only judge from youtube as one never crossed my path. Sadly they never demo the reverb on these amps.

43

1) Does the ticking become less ... or less treble when you engage the after beat switch to on ?

The ticking is not there when in normal tremolo mode. It starts ticking when you engage the afterbeat. I think the afterbeat works by loading up a capacitor and then dumping off its charge all at once, which is probably very prone to getting picked up on nearby audio lines.

2) Does the ticking disappear or become less pronounced if you remove the Reverb drive tube (V6 6CG7) ?

I've not tried this, but I suspect it has more to do with my lead dress than anything inherent to the circuit.

3) Or disappears when you disengage reverb ?

Yes the ticking is there regardless of the reverb setting. To be honest I don't really use the afterbeat. It's a very choppy, synthy sound, kind of like the beginning of "Won't Get Fooled Again", but not as good. It's kind of fun for messing around, but not terribly useful to me otherwise, especially with the volume drop.

4) Just want to make sure; Does it self oscillate when you turn the "Dimension" control up ?

Yes, "Dimension" is what the person who drew that schematic labeled the reverb mixer control. On my amp, it's labeled "Echo Ch 1".

The schematic I posted (click here ) seems to be for your amp, but it doesnt have a 1M resistor across the lamp so maybe my questions above would not be valid as the circuits used may be different.

The resistor is there in your schematic, just a little harder to spot (look above the "afterbeat" circuit). Indeed this schematic is why it took me so long to realize it wasn't there in my amp. I find the factory schematic (https://ampeg.com/support/f...) a little easier to read.

44

Gibson GA79-RVT stereo amp. Adding to the effect is that the reverb tank is mounted vertically. Volume and bass set to zero and treble at 10: "100% reverb".

45

Otter;

Ok then I misunderstood you. Weird that it only starts ticking with the afterbeat on. Should be real easy to fix though. My other questions were just to see how the tick enters the audio path. There are only two ways it can enter. As you can see from my schematic, the supply voltage for 1/2 of the reverb 6CG7 (V6) is the same supply for the Oscillator V7A. If the 40uF 450V capacitor is shot clicks will leak to the reverb circuit , but you seem to say disengaging reverb does not get rid of the clicks, so it wont be that then. That leaves you with a bad ground somewhere in the circuit, or it somehow enters through XY (the latter which I doubt). The self oscillation issue might be the lack of grid resistors in the design and might go away using a different brand tube without adding grid resistors. Anyway, if ever you need extra opinions when you decide to fix it, you can contact me through GretschPages PM (if it works as I havent used it yet).

nielDa;

Now you are talking. The GA79-RVT has been on my list to buy for quite a number of years. Most Unique amp and completely underrated in my opinion. It has everything fixed what I disliked of the stereo magnatones.

46

Otter; Here is an annotated schematic that shows what I mean. (note that the blue line goes through E, but is not a connection I consider. Only "C". Too simple to correct now). Unfortunately the image was reduced in size uploading it. Hope you can read it.

The big problem I see is that the Tone circuit output is very high impedance, which will allow a feedback loop for the reverb (the RED path). If the tone was buffered or at least driven by cathode follower, feedback would not be possible and in the latter case much less likely. I think that is the problem for the self oscillation. It can be fixed, by adding a component or two, but sometimes a lower gain tube in the reverb will solve it. I would try an At7 or Au7 in the V7 position first as non-intrusive solution to tame feedback. If that helps you can trace the circuit and see if a DW7 cannot be used so that the AT7 part is on the reverb and the 12AX7 part is on the oscillator. But a first try would be an AU7 or AT7 or AY7 in V7. I would try all three for the lowest gain/phase option and see if it doesnt resolve. .

Another option to try is to swap the wires of the output of the echo unit (if they are floating! and one is not connected to e.g. ground. ). This will change the phase by 180 deg and if you have a positive feedback issue currently, it will become negative feedback and the auto oscillation thing may disappear. Just be careful to check that the output of the "echo unit" is floating. I have no clue what tank you have or if it is possible with the tank. If it was solder wired up, then they might have switched wires the wrong way at the factory and created a positive feedback loop unintentionally.

I am reasonably sure the AU7/AT7/AY7 in V7 might do the trick (or the reverb output wire switch) as the former will dampen some of the obvious grid resistor issues in the design and reduce the gain and thereby the feedback. You can also try a AU7/AT7/AY7 in V6 if you have an adapter.

I also annotated the others issues we discussed. Blue line shows that if the supply capacitor is leaky you have a path for clicking as discussed in my previous post.

When you have time in future, remove the 1M resistor again just to see if the clicking disappears when you engage the afterbeat. It might be that they had this problem in the factory and decided to fix it by removing the 1M and send the amp out of the door rather than to trace the error. If it disappears with the 1M removed, I am sure that is what happened and will account for the missing 1M. Otherwise a bad ground somewhere definitely can cause it and if I read your response correctly you already suspect that with "dressing remark".

7199's are absolute classics and I love them since my youth (Dynaco days) and hard to come by or expensive. Dynacos is still some of the best HiFi pre and power amps you can get. The 6GH8 with adapter can be used in place if I remember right and since the 7199 is not used in a high gain situation in your amp there should be no loss in quality.

Nice amp though. The Pentode Triode 7199 in the design right is out of the HiFi design books and is high quality design IMO.

Anyway, hope it helps. That is where I would start looking.

47

Thanks for all the advice. I will definitely look into these things when I open it up again, but I suspect it will be some time. Don't have any AT7 or AU7 tubes handy.

To be honest, I don't really consider the reverb feedback a problem, just don't turn it up very high. From what I've read, most of the Geminis are this way, and I believe it's acoustically-coupled. It's not really runaway feedback the way an analog delay pedal does it, more of a hot-mic type of a sound. Just don't turn it up much, it's already plenty of reverb before you get halfway on the knob, and very good-sounding.

Without the 1M resistor the tremolo is very weak. Indeed it did not tick, but it was not a very useful tremolo like that, so I'm inclined to keep the resistor. In my experience (mostly Fender amps), ticky trem can usually be solved with responsible lead dress.

48

Definitely place the resistor. I did not suggest you leave it out. All I pointed at is that if the ticking disappears when the resistor is missing, then it strongly suggests that they omitted the 1M for that reason during QC rather than to chase down the real source of the problem. This happens in all production environments regardless of brand.


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