Submini Tube Reverb request

[tubegeek]

but the 6N21B can't seem to wobble those springs by itself.

That seems suspicious to me - I'd expect a poorly matched driver to have WEAK signal, but not NO signal. Is it possible that the way the jack is wired at the reverb input is shorting out your send signal going into the tank? I know that some tanks are floating input, some are grounded input, etc.

Also: are you sure this tank has worked in the past/is working now? Getting output but no input could be a sign that the fragile input transducer has been damaged. By shaking the tank you are testing the output transducer but not the input transducer.

Finally: is the tank equipped with a shipping lock that traps the springs? That's also an available option on some tanks - I think there's a lever that accomplishes this?

Apologies if you know all of this and have taken it into consideration, there are just some possible pitfalls with reverb tanks that aren't always obvious so I thought I'd stick my nose in.

[vigilante397]

Is it possible that the way the jack is wired at the reverb input is shorting out your send signal going into the tank?

Nope, checked that one.

are you sure this tank has worked in the past/is working now?

Also nope both tanks came out of amps that had been sitting outside on a covered patio for 30 years or so. That was a thought I had, I can't guarantee the working order of the tanks. I was hoping they were good, because I really don't want to buy a tank

[tubegeek]

are you sure this tank has worked in the past/is working now?

Also nope both tanks came out of amps that had been sitting outside on a covered patio for 30 years or so.

Hmm. Do you have a signal generator? You see where I'm going with this... I know I don't work anywhere near as well as I did 30 years ago, and I usually get to sleep indoors.

[vigilante397]

You see where I'm going with this...

I do indeed, you're telling me I need to spend more than 5 minutes working on it I don't have a signal generator at home anymore, but I have access to one at work. I'll bring the tanks with me to work tomorrow and plug them in after everyone else leaves, see if I can get them to wobble.

[Ben N]

I really don't want to buy a tank

You sure you wouldn't reconsider?
https://tanks-alot.co.uk/military-vehicles-for-sale/

[vigilante397]

I really don't want to buy a tank

You sure you wouldn't reconsider?
https://tanks-alot.co.uk/military-vehicles-for-sale/

So this still works toward my point, I want to own a tank without paying for a tank I would love to have a tank parked in my front yard as a warning to neighborhood kids to stay off my lawn, but I don't want to spend money on it.

[tubegeek]

I would love to have a tank parked in my front yard as a warning to neighborhood kids to stay off my lawn, but I don't want to spend money on it.

Did the kids ever give you any trouble with trespassing in your covered patio? You have pretty relevant, pretty long past experience to draw from there!

[vigilante397]

Did the kids ever give you any trouble with trespassing in your covered patio? You have pretty relevant, pretty long past experience to draw from there!

These amps weren't from my patio, I rescued them (and a couple hundred tubes) from a friend's junkpile of a yard. I've barely been alive 30 years, and only 20 of that has involved collecting guitar-related garbage

[Ben N]

I would love to have a tank parked in my front yard as a warning to neighborhood kids to stay off my lawn, but I don't want to spend money on it.

All you need is a Gran Torino.

[Greenwichpaul]

Do we know anythign about the tanks you have, what impedance they are  etc etc etc?

Can you borrow a known good tank and/or transformer, to validate if the mini tubes actually work?

[vigilante397]

I have the part numbers and I looked up the tanks, looks like I wrote a while back that the input on one of them is 2k, I think the other was around the same. I said I would bring them in and test them with a signal generator and I keep forgetting to do so

If I lived in a big town with a decent music scene maybe I could borrow a tank, but I live in a small town with no music scene, so I don't know anyone with a tank lying around. I'll try REALLY REALLY hard to remember to bring the tanks in to test them tomorrow, and if they don't work I guess I'll just bite the bullet and spend $30 on a tank so I can wrap up this project

[vigilante397]

It's been a couple months, time for an update on this. I finally remembered to bring the tanks in to work a while ago, but the signal generator was left hooked up to something else and I didn't want to risk unplugging it from that to test my tanks, so they still have not been tested.

But I've been working on a different submini tube build for a customer (JCM 800 preamp, turning out really cool), and last night he asked me if I could also do a submini tube reverb So I ordered a 9AB3C1B tank, which is the one called out in the build I based mine off of, and in a week or so I expect to be able to say definitively whether or not these boards I have are good.

[vigilante397]

IT WORKS.

The new tank came in today and I got everything hooked up tonight. I can't really crank it because the kids are asleep, so I may try to get a quick demo tomorrow after work, or I may just box the thing first and then do a demo, we'll see. But anyway, observations:

- I'm using a long decay, three-spring tank so it gets WET.
- It has some buzzing on the reverb setting (not on bypass), could be due to the fact that it's not in a lovely metal box yet.
- The clean signal is noticeably quieter on the reverb setting than the bypass setting, which is also kind of understandable looking at the schematic. Personally I would probably increase the gain on the clean section and make it true bypass rather than a tube-buffered bypass.

Anyway, it's been a loooooonnnnnggggg time coming, so thanks for the gentle reminders every so often, sometimes I need that

[Ben N]

OK, Nathan! Too hard to keep track, but what do you have driving that thing in the end? I'm seeing four tubes and a transformer. What are they and how are they configured?

[vigilante397]

So I stuck with my original plan of four 6N21B tubes, and I'm using a Hammond 125A transformer, which isn't ideal since it's a PP transformer and I'm using it as a SE, but it gets the job done. A proper SE transformer for this can be had for about $18, but I have a handful of 125A lying around from other projects.

I'm at work so I don't have my schematic in front of me, I'll post it when I get home, but I pretty much copied this schematic, just substituting all the tubes for 6N21B, dropping the plate voltage, plus running heaters at 12VDC and using each pair of tubes like a voltage divider to get 6V per heater:



You can find the pdf version of the schematic here: https://www.modkitsdiy.com/sites/modkitsdiy.com/files/media_files/k-mod103_schematic.pdf

[PRR]

> some buzzing on the reverb setting (not on bypass), could be due to the fact that it's not in a lovely metal box yet.
> The clean signal is noticeably quieter on the reverb setting than the bypass setting, which is also kind of understandable ...

Yes, you need a lovely metal box. The spring return signal is generally less than guitar level. And you know how much buzz you can get, guitar-effect open on the bench instead of a lovely metal box.

I have suspected this reverb was rushed to market, to cash-in before the fad for reverb went out of style. Also that most guitarists of the day were less fussy about gain (that's what knobs are for). While Leo went on to build-in a better reverb scheme integrated into his amps, I think if he'd re-thought the standalone reverb he would have thought again.

I also think *that* plan is mis-copied from Fender:
https://robrobinette.com/images/Guitar/Other/Fender_6G15_Annotated_Schematic.png
(note output network) but flawed either way.

[Ben N]

I have suspected this reverb was rushed to market, to cash-in before the fad for reverb went out of style. Also that most guitarists of the day were less fussy about gain (that's what knobs are for). While Leo went on to build-in a better reverb scheme integrated into his amps, I think if he'd re-thought the standalone reverb he would have thought again.

I also think *that* plan is mis-copied from Fender:
https://robrobinette.com/images/Guitar/Other/Fender_6G15_Annotated_Schematic.png
(note output network) but flawed either way.

Do tell. I have never encountered a standalone Fender Reverb in the flesh, so I know only the mythology.

[snufkin]

wow I cannot wait to build this :3

[vigilante397]

So I didn't get around to boxing this over the weekend like I planned (I'm working on another project that will probably pop up in the lounge at some point this week) but I'm working from home until further notice, which means it's a lot easier to get stompbox stuff done over lunch breaks and such, so I expect to have a boxed prototype of this finished sometime in the next couple days.

Chris, I got your email, I will absolutely sell PCBs once I've satisfied myself that this is working properly. Last time I sold through-hole PCBs I rushed to get them out and made mistakes, trying not to do that again.

[danielzink]

Hey there !

Any more progress on this ?

I realize it's been a crazy year (and a half)