It is currently Mon Mar 16, 2020 1:09 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 8 posts ] 
Author Message
Post subject: Need some tube help on Dual Showman Reverb
Posted: Fri Feb 06, 2015 3:54 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Dec 18, 2013 5:19 pm
Posts: 75
I am swapping some preamp tubes around in my 73 Dual Showman Reverb but I have little knowledge when it comes to 12AT7s. I have what appears to be an old RCA 12AT7, two Amperex 12AT7s that say Great Britain, yellow lettering and a globe printed on them and a couple of JJ ECC81 tubes. In the PI slot I tried one of the Amperex tubes with the RCA in the reverb slot. Sounded ok but seemed like it wasn't as clean as it should be and the bass notes seemed kind of sloppy. I then put the RCA in the PI slot and it seemed to tighten up the sound and cleaned it up a bit. In the reverb slot I tried a JJ and then a Amperex and I am not sure what to listen for or which tube is better suited for that position. First of all is it just my imagination that I am hearing a difference in tone switching the PI tube? Been 40 years since I owned a old Fender tube amp so please bare with me. Also what should I be listening for switching tubes in the reverb slot? Thanks for any help or pointers.


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Need some tube help on Dual Showman Reverb
Posted: Fri Feb 06, 2015 4:49 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Dec 18, 2013 5:19 pm
Posts: 75
Well I have been going back and forth between the RCA and Amperex in the PI slot. What I hear is the RCA sounds cleaner and brighter and tightens the bass up somewhat. The Amperex still sounds clean but seems warmer, takes some of the edge off the highs, loosens the bass up but has more punch with a tad of grit when I hit the strings hard. Either that or I have one hell of an imagination. Still not sure which I like. The RCA to me sounds more like I would think a Twin or Showman would sound but at the same time I love the warmth and punch the Amperex has. Still not sure how good a tube the Reverb tube has to be but right now I have the other Amperex in that slot.


Top
Profile
Post subject: Re: Need some tube help on Dual Showman Reverb
Posted: Fri Feb 06, 2015 5:29 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Tue Mar 01, 2011 3:10 pm
Posts: 5646
Location: Gateway to the West
Sounds to me like you have the process for figuring out how to select the "Right" tube for your reverb. Some like their reverb a bit warmer, while some like the clean ring and splashiness. I am not sure we can help you as it is purely a thing of taste.

I like my reverb big and splashy. So the crisper cleaner tube works for me.

T2

_________________
-----------------------------------------------------------
What time is it? It's Fender Time.


Top
Profile
Post subject: Re: Need some tube help on Dual Showman Reverb
Posted: Fri Feb 06, 2015 6:39 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Dec 18, 2013 5:19 pm
Posts: 75
T2Stratman wrote:
Sounds to me like you have the process for figuring out how to select the "Right" tube for your reverb. Some like their reverb a bit warmer, while some like the clean ring and splashiness. I am not sure we can help you as it is purely a thing of taste.

I like my reverb big and splashy. So the crisper cleaner tube works for me.

T2


Know what you mean. Guess my ears have been answering my own questions. Still curious though how good does the reverb tube need to be. Chinese 12AT7 or something better like a decent NOS? Thanks


Top
Profile
Post subject: Re: Need some tube help on Dual Showman Reverb
Posted: Fri Feb 06, 2015 7:00 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
The 12AT7 reverb driver needs to be a very good tube. IME. Fender amps are notorious for pushing this tube, the hardest, of all tubes in the amp's lineup. Both anodes of the duo-triode are tied together. A full 425-440VDC (with today's outlets) is placed onto these plates. It is not uncommon for an idle bias of 10-15mA, in Class "A" setup. Max ratings for most 12AT7's.

Often, at these settings the tubes fail early, get hissy, or microphonic.

I like mil spec 12AT7WA, WC, or 6201 in this position. Sylvania/Philips 12AT7WC or Siemens/Philips 6201 (E81CC) are the best for this job. Good numbers of NOS are still available. No new production 12AT7 can match these older tubes, in terms of toughness and long, quiet life.

In contrast, the 12AX7 reverb recovery tube is not pushed hard. I've found that tube rolling this tube, can have the greatest effect on the reverb tone. The new TSRI 12AX7 give the brightest tone. New issued Gold Lion 12AX7/B759 the warmest. A good RCA 7025 the best tone.


Top
Profile
Post subject: Re: Need some tube help on Dual Showman Reverb
Posted: Fri Feb 06, 2015 7:23 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Dec 18, 2013 5:19 pm
Posts: 75
Great info! Thanks.


Top
Profile
Post subject: Re: Need some tube help on Dual Showman Reverb
Posted: Sun Feb 08, 2015 5:07 pm
Offline
Amateur
Amateur

Joined: Sun Jul 25, 2010 8:13 am
Posts: 147
Location: Charm City
Hi lovehifi, and welcome. I'm also a big fan of the DSR, and own a very early one, a '68 TFL 5000D with aluminum drip guard.
As has been noted, there never was a "blackface" version of this amplifier, it was one of the first of the new "silverface" models Fender introduced. It is however, a fairly easy job for a good tech to bring earlier versions of this amp to something similar to the vaunted AB763 Twin Reverb specs. As you know, it is essentially a Twin Reverb in head form, and has the benefit of only weighing about half of what a Twin does. The mods involve adding a bias pot (optionally removing the hum balance pot), changing some cap and resistor values while removing others, and cleaning up the extraneous wiring.
The choice of cabs and configurations is endless. I also like the Emi Legend 1258's as a 2x12 option, and I agree with the mud/darkness of the Celestion G 12 T 75/100's- I had a 4x12 cab with these drivers, and they just didn't seem to work very well with the Showman-they lacked any high end sparkle. I've also got a homemade 2x12 cab with a pair of '60's Orange label Utahs that match well with the amp.
My current project is building a 1x15 with a JBL D130F, the original go-to speaker for the Showman.
You will find a wealth of information on this forum from friendly, experienced people who are always happy to share their expert knowledge of vintage Fender amps to those new to the hobby of collecting, repairing, modifying (and maybe even occasionally playing, hah!) these great amps.


Top
Profile
Post subject: Re: Need some tube help on Dual Showman Reverb
Posted: Mon Feb 09, 2015 5:15 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Dec 18, 2013 5:19 pm
Posts: 75
Thanks. I actually cleaned up the head cabinet and put the amp back in to that. I also found several NOS 12AT7s and 12AX7s that I had left over from my Ham radio days and did some preamp tube swapping and found the combination that sounded best to me. The tech that I took it to when I had it checked out did a bias mod that he says he does to all these older Fenders. Might be what you are talking about. I know he said it had something to do with the hum balance pot and adding something else. I absolutely love the sound of the amp and the 1258 speakers sound great to my ears. I might look at some of the other mods one day as you pointed out but for now I am just going to sit back and enjoy its beautiful sound.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 8 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: Google [Bot] and 1 guest


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: