It is currently Mon Mar 16, 2020 9:07 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 3 posts ] 
Author Message
Post subject: '63 RI Reverb Unit mods
Posted: Thu Mar 29, 2012 11:18 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Did not get around to "processing" photos in my digital darkroom, yet. :mrgreen:

One note of caution!

The RI Reverb Unit has the thinnest and cheapest circuit board and tracings of nearly any amp I've worked on. Extreme care is needed to work on this unit. I did most of the swaps by cutting ONLY the main body of the component and leaving the leads in the board. Then, soldering the new cap or resistor onto these leads.

I had to pull a few items out of the board. Best to cut the component's body off the lead. Pull the board OFF the chassis. CAREFULLY heat and remove the remaining wire (don't heat the tracings!!!). Use as low heat as needed to unsolder the wire. And when you go solder the new part-- you may want to practice on a few parts off the board-- to get the heat range correct. You do NOT want to heat that board any longer than necessary. Overheating = fried tracings.

If you do damage the board--- stop and fix the broken tracings first. Or you can end up with an irreversible mess. There! You've been warned.
:D


The RI requires quite a bit of work to "open" up the midrange, ala a 6G15. I replaced the 250 pico-farad on the output with a 250pfd/630VDDC silver mica-- that helped, but mostly mids-to-highs.

Changing a couple of the generic "unlabeled" coupling caps helped a lot. Esp (C1) 0.01 mfd/400VDC & C3 0.0022mfd marked as 600VDC on schematic, but a 400 VDC in the circuit. Nothing fancy. A Mallory-150 is fine.

Oddest OEM caps found were C2 & C4. A 22mfd/35VDC (!?!?). Plain old 25 mfd/50 VDC make a BIG difference in mid-to-low frequency response. It is a cap you people prolly have, up to your ears in stock. I have no idea why Fender used a 35VDC rated cap here. As they must have a million 25/50 lying around.

And C4 (again, 22mfd/35VDC) is way under-rated as the bypass cap under the 6V6GT cathode. A 25/50VDC is fine. I went to a 22mfd/160VDC F&T, not for voltage rating, but for added heat and current stability of the extra VDC rating. I happened to have some. I do not believe AES carries either the 22mfd/160 VDC F&T or the 25mfd/250VC Sprague Atom. I got mine from Parts Connexion. Also, changed C7 from 220mfd/16VDC to 220mfd/50VDC (Panasonic PIO).

In this unit, the best 6K6GT still does not sound too good. I think that the 12AT7, as the input tube, just does not produce the swing (at least the way it is setup in the RI Reverb), compared to the 12AT7 input of the original 6G15. Alternatively, the current push in the original maybe much greater. This prolly is the case. As the 6G15 as a much bigger PT than the RI. The RI's PT is no bigger than the OPT used to drive the tank.

You need the strongest testing 6V6GT (in fact, you can use the unit as a tube tester---it is that sensitive), to adequately drive the OPT and tank. I ended up with a GE mil spec brown base 6V6GTY. Which I know prolly puts out healthy 15-16 clean watts. These and the Raytheon gray glass 1950's GTY are the most potent 6V6GT's I know of. Then, the 1950's BP TungSol 6V6GTA. I remember that the RI's I replaced the 6V6GT with a 6K6GT had 12AX7 or 5751 in the input stage. Which accounts to bigger swing. But, prolly won't last as long as the 12AT7, under heavier current load.


Oh and the original tank? It makes for a nice paperweight. LOL! No comparison to NOS Accutronics. I am using one out of a 1967 Princeton Reverb, I had lying around. (4AB3C1B).

Then... you get a unit comparable to the 6K6GT driven 1960's Reverb Unit.

http://www.webphix.com/schematic%20heav ... manual.pdf

http://www.webphix.com/schematic%20heav ... _schem.pdf


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: '63 RI Reverb Unit mods
Posted: Thu Mar 29, 2012 6:24 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Seems like a daunting task, Beemer! Haven't had the pleasure of repairing a PC board amp for years. The last was a Champ 12, a neat little single-ended amp. Your patience must be in pretty good shape, man! Art

_________________
None of Us are free, if One of Us is chained !


Top
Profile
Post subject: Re: '63 RI Reverb Unit mods
Posted: Fri Mar 30, 2012 7:46 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Prolly can get away with one cap change (the 250 pico-faraad to silver mica), a better tank, and a strong testing 6V6GT, maybe even a the 6V6S. But, you'll just have the extreme settings of a good 'verb unit. Not the great range of the original unit.

I started out with simpler changes. Without going to a new tank or output tube. But, ended up going that route, eventually. The coupling cap did help some of the adjustments range. But no where near my beloved 1966.

The important lesson here: BUY a good used 6G15. They are easier than sin to work on. All parts are readily available (except the US made tanks). The cheap NOS 6K6GT work superbly in the unit. And it sounds better, with much more range than the '63 RI Reverb Unit.

I have both a 1966 6G15 and the RI to compare side-by-side, and after a good 6 hours of modding the RI sound ALMOST as good as the 6G15. Not the fine tuning range of the original. But, at least I got the dripping wet tone and the "touch" of 'verb so important for most amps. If I never see one of those crazy 50¢ circuit board again, it'll be too soon.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: