6G15 Reverb

[Mark]

https://tubeamparchive.com/download/file.php?id=2036

This circuit diagram could have a few good pointers. Notably the return stage and backing off the gain in the send stage. I'd look at ditching the 12AT7 and use one 12AX7 triode, then use the the remaining triode in the return stage.

All food for thought.

[Kazooman]

Thanks Kazooman!

I've heard people try to describe how these tanks are supposed to be mounted, but it actually took your pics to wrap my mind around it. I will be referring to this thread a lot in coming hours as well as weeks...

The key to mounting the tank is to find appropriate springs. They need to be strong enough to hold it suspended in air, but light enough so that the tank is really floating. It takes almost zero pressure to push the tank down to the cabinet. Also make certain that the mounting posts give enough side to side clearance.

The locking mechanism, if you try to build one, is just sort of a U-shaped piece of metal. The side that is against the cabinet has two slots that ride on screws. One slot is L-shaped. You push the lever forward and then slide it sideways so that the screw for the L-shaped slot is trapped in the leg of the slot. I can take a better picture of the lever if anyone wants to see one.

[bcmatt]

I imagine it shouldn't be hard to find some sort of piece of something to make the locking mechanism. I am a bit concerned about being able to find springs for mounting the pan though. I can find an appropriat pan with the right impedances at AES but I don't see any mounting springs for sale for reverb units. Perhaps I have reverb springs I could use from old replaced pans. Would they be about the right tension?

It looks like I won't be able to build this for at least a couple months. I am not in the right part of the country and won't be able to build the whole thing before the big August tour, so I probably have till September now to source all the parts for this thing...

[Kazooman]

quote="bcmatt"]

I imagine it shouldn't be hard to find some sort of piece of something to make the locking mechanism. I am a bit concerned about being able to find springs for mounting the pan though. I can find an appropriat pan with the right impedances at AES but I don't see any mounting springs for sale for reverb units. Perhaps I have reverb springs I could use from old replaced pans. Would they be about the right tension?

No, the actual reverb springs would be way too light. I found the springs for my unit at a local hardware store. I'm not talking about a big box store like Lowes or Home Depot, I mean a REAL hardware store. They had hundreds of springs to choose from.[/quote]

[jon]

Here is the reason you should never buy parts kits. I bought a package off the TAG consisting of a PT Choke OT and Chassis and Reverb Tank. It was a great deal. I got the parts and started building, never even checking the P/N# to see if the transformers were correct. Turns out that I had a Champ OT not the correct Reverb driver.

To summarize my build was correct my parts were wrong. I'll have it fixed tonight as I have the correct iron on the shelf.

[Mark]

Hi Jon, What was the difference in spec and tone?

I thought the Reverb tranny was a lower impedance than the Champ tranny.

These are the transformer numbers I have PWR: 125P24A or 012671, choke 125C1A or 022699, O/P: 125A12A or 022990.

The choke is quite common, but the other two transformers aren't. Personally, I don't know why Fender chose half wave rectification?

http://www.ebay.com/itm/N-O-S-1966-Fend ... 500wt_1156

[jon]

Reverb transformer is 8K to 8ohms

Champ is 8K to 4ohms

[bcmatt]

I'm trying to source parts for this build finally (after talking about it for a couple years (my EH Holy Grail pedal finally crapped out so I figure it is a sign it's time)).

Anyways, I often try to get all my parts from AES to save on shipping but I can't really find a suitable Reverb Driver such as the A125A12A. IN fact, I there isn't anything 8K to 8 ohms. Anyone find anything?

I've seen someone suggest this one somewhere:
http://www.tubesandmore.com/products/P-T1750B
It's about 5K5 to 8 Ohms. Do you think using a 6V6 instead of the 6K6 would help make the lower primary more appropriate? Or would that cause other issues in the circuit?

[irv78]

When I built my 6g15 I've spent some time on finding information about the 125A12A transformer ... this is all I found:

*archive-ampage-org*
> http://archive.ampage.org/articles/4/ga ... ments.html

> Part number 125A12A as used in the 6G15.
> Turns ratio 30.15:1
> Calculated impedance ratio 909:1
> Therefore, assuming an 8 ohm reverb tank input transducer, the primary
> impedance would be 7,272 ohms.

The transformer I bought in the end was the Hammond 1760C. With the 8 ohm tap this transformer is with 7.000 ohms as close as you can get to the original 125A12A transformer.

Hope this helps! Cheers, irv

[bcmatt]

Thanks Irv!
I emailed Antique Electronic Supply about the 1760C because I couldn't find it on their website and I was planning to get the rest of my components from them (being in Canada it saves a lot to have everything sent together).

Do you use a 6K6 with yours, or a 6V6? I'm assuming 6K6 because that is the original and they can be had for about half the price of a standard quality 6V6.

I wonder what people that use 6V6s find in their tone... any difference?

But anyways, the schematic says 285V on the plate of the 6K6 and you pointed out the OT primary impedance would have been about 7k3.
For a minute I'm going to pretend I can understand tube charts and read this which I think says it hopes to see about a 7K6 load at 250V and 9K at 315V so let's go halfway to be lazy and say it suggests about 8K3 around 285V:
http://www.tubebooks.org/tubedata/HB-3/ ... 6K6-GT.PDF
So the original Fender transformer gives it about 1K or 13% less than the supposed ideal rating.


So, if I was to use a 6V6, let's grab the same crazy assumptions from this chart:
http://www.tubebooks.org/tubedata/HB-3/ ... V6-GTA.PDF
...which I think says it hopes to see about a 5K load at 250V and 8K5 at 315V so let's go halfway to be lazy and say it suggests about 6K7 around 285V.
So, if we were to assume that a 6V6 reacts similarly to being under-loaded by the same percentage (which I doubt), we would shoot for about a 5K9 primary impedance...

So, in that case the 5K5 to 8ohm impedance of the Hammond 1750B might be more ideal for a 6V6...
But what is considered ideal? Is that for max power at the voltage or some specific tone? perhaps that would drive the reverb pan too hard? I don't know? I'm curious to know opinions...

I guess the ideal situation is to replicate the original and try to get a 1760C to use with a 6K6. maybe what I can save on buying a 6K6 instead of 6V6 would pay for the extra shipping to buy the 1760C somewhere else...

Since Hammond is Canadian, you'd think I could get their transformers cheaper here, but that's rarely how it works in Canada...

[bcmatt]

so apparently AES will special order the 1760C and they will sell it for $44.10. It requires a 50% deposit and it will take about an extra 3 Weeks for them to get it.

[irv78]

Yes, I use a 6K6 because that tube was meant to be in this circuit.
I was after the sound of the original units so I tried to stay as close as possible to the specs.

I also have a re-issue reverb unit where I swapped the stock 6V6 for a 6K6.
To my ears the 6V6 sounded agressive and harsh. The 6K6 is a bit mellower and gives the controls a more useful range.

IMHO, YMMV, of course

[rp]

so apparently AES will special order the 1760C and they will sell it for $44.10. It requires a 50% deposit and it will take about an extra 3 Weeks for them to get it.

try also Angela or http://www.radiodaze.com/

Long ago I messed up a few Fender BFs and SFs thinking it would be genius to replace the crappy discs and resistors with films and mfs. Destroyed the sound, made it hard and bright and 'too much', the last being weird but it was so.

As stated getting the pots right matters a lot.

The old pans were all different - from amp to amp, maybe from age maybe from poor tolerances. I used to swap and mix and match among amps and reverb units until a got a particularity fine mix and then kept that one for myself. It helped that Fenders were cheap then (enough anyway and I had less bills) and I had friends with music stores. I'm betting the new units aren't any more consistant.

[cobalt]

I have a RI on my bench.....
He said "It keeps blowing fuses".
Well I opened it up, didn't see anything wrong, so I put in a new fuse. Plugged it in, turned on, and it blew the fuse.
Next I pulled the HT pair.....NO continuity.
Then pulled the filament......continuity.
Then pulled the primary.....No continuity.
Ok busted PT. Something caused this.......caps or OT or pooched 6k6?
I am ordering caps, will test OT tomorrow.
The question I have is on PT which one?

http://www.tubesandmore.com/products/P-TF47609


http://angela.com/fenderreverbunitpowertransformer.aspx

Thanks Bunches!
weirddave

[bcmatt]

Thanks guys,
I'm really looking into all these transformer options today,and second guessing everything.
The Half-wave rectifier vs Bridge rectifier is throwing me off since I really don't know about that stuff. The Reissues use a bridge rectifier, but does that boost the voltage significantly? Do they use the same PT?

The question I have is on PT which one?

http://www.tubesandmore.com/products/P-TF47609


http://angela.com/fenderreverbunitpowertransformer.aspx

Thanks Bunches!
weirddave

As far as these go, they have the same transformer code so you'd think they should have the same specs, but the Hammond one at AES is about $15 cheaper at only $26 instead of the (Fender?) one for $40 at Angela. The Hammond says it is for the 63 reverb but the Fender at Angela states it is for the reissue. Are they the same? Could you use a bridge rectifier on both?

The Chokes same the most straight-forward. Hammond194B is to spec and available at either place for $18. The Fender choke is only $13 at AES but is back-ordered.

Things get a little more interesting again for poverty stricken musicians like me when it comes back to OTs.
I found this about the 47605 at Angela for $14:
http://archive.ampage.org/threads/1/ope ... erb-2.html
29:1 ratio with a primary of 6k5 potentially does not seem too bad when you get to save another $25 compared to elusive 1760C at $40. I don't know... what do you guys think? It would be trusting another person's calculations. I guess this is the difference between the reissues and the originals as far as difference in tone...