|
Dirty-South Blues Harp forum: wail on! >
power tubes for bassman reissue 5881 or 6L6
power tubes for bassman reissue 5881 or 6L6
Page:
1
528hemi
335 posts
Dec 03, 2012
1:12 PM
|
What brands are preferred and do most go with the 5881 or 6L6?
528hemi
|
Rick Davis
952 posts
Dec 03, 2012
1:30 PM
|
I use pretty basic tubes: new prouction Tung Sol 6L6 STR. I tried 5881 tubes but I thought the 6L6s were a bit warmer. It is all totally subjective, and there are so many moving parts in the Bassman tone that changing one component may not make much difference.
Tube Depot
----------
-Rick Davis
The Blues Harp Amps Blog
|
5F6H
1438 posts
Dec 03, 2012
2:19 PM
|
I tend to feel that one of the bassman's plusses is its punch & tend to like tubes that support that, I avoid the EH6L6 & SED/Winged C 6L6GC as they can be a bit blurry & compress the front off the note, but not in a way I like, note separation gets a bit unintelligible. Might be better for recording/low volume than stage work.
NOS Philips 6L6WGB are the 'go to' vintage tube, I normally like the sturdy Sovtek 5881WXT, though some dislike it as harsh, it has a tighter high end than the Phillips. The TAD 6L6WGC is my favourite of the modern small bottle 5881 style tubes, but these are on the dark side. JJ's? I prefer them in a 2x10 running hot, can be a little sterile in a 4x10" at moderate currents.
The most important thing is to try what tubes you have at a range of bias currents to see how you like the sound & how much current you can use before feedback becomes a problem (more current = more gain in the output section). There is no "right" bias current, there is just what works best with your tubes, amp & your tonal preference (the only concern is to not run them so hot they die early). I tend to start around 15mA per tube, then try +5mA & -5mA to see which way you want to go. More current "sings" more & can be more chimey, lower currents crunch more & feedback less.
Treat current production tubes as 25W despite what the manufacturers blurb says...the JJ's are 30W tubes, but in a bassman there is little benefit in really pushing the current, you shouldn't need to exceed more than 17.5W dissipation at idle.
----------
www.myspace.com/markburness
http://www.facebook.com/markburness
Last Edited by on Dec 03, 2012 2:20 PM
|
528hemi
336 posts
Dec 04, 2012
5:41 AM
|
Thanks Mark,
On a different topic, When I add the Bias Pot and replace the 2 resisters to 1 Watters, I did not open the amp and check the circuit board but I assume the solder pads are on the bottom of the board?
If this is correct, Is it easy to desolder the resisters. Do I need to take the chassis out remvoe teh ciruit board to get to them. I saw a picture of some ones modded amp and it looks like they cut the resisters out and left the wire ends and soldered from the top of the board. They is cludgy.
Thanks
528hemi
Last Edited by on Dec 04, 2012 5:43 AM
|
5F6H
1440 posts
Dec 04, 2012
6:41 AM
|
You are welcome to remove the circuit board (and control panel PCB, and input jacks) to do the work if you like...it is not absolutely necessary, nor usually cost effective to do so if someone just has a failed resistor that needs replacing.
Welcome to the world of PCBs! ;-) I hate working on them, but the Fender RI's are far from the worst.
Piggy backing resistors/bypass caps on to existing resistors is pretty straight forward, work fast, not too hot an iron (if you have a temp control, or use a smaller iron) just enough heat to get the solder to wet & make a good connection.
If you are replacing a resistor altogether you can piggy back to the existing part, leave some excess lead length around the original part, then carefully snip it out. The solder connections you make here will have good integrity and the original component will absorb some heat making it less likely that you will cook the original solder. Sometimes it's possible to make a more solid connection by jumpering existing , sturdy, parts like big caps & spade lugs.
If you are replacing an intermittent part, it's best to drop the board - sometimes resistors heat up, expand, cool & shrink and desolder themselves...in these cases tacking on means you are tacking on to an intermittent joint on the back of the board & it won't fix the problem.
The RI's aren't too bad, they can stand the boards going in & out...some other PCB amps aren't so tolerant and you run as much risk of causing other damage, especially where PCBs are very crowded (some only have a hair's breadth between traces & solder blobs at hundreds of volts difference in potential). It's your amp, you aren't going to charge yourself a lot of money to do the work so drop the board (make a diagram of any wires you remove from the board).
If you are taking the board out, you may as well upgrade all the plate resistors R28, R29, R14, R8, R9 (1W) and the screen grid resistors (use 2-3W types, raised off the board) R33, R32.
R14, R28, R32, R33 are the most likely original parts to fail...even though this happens very rarely, if you have the board out, I'd take the opportunity to bullet-proof the amp.
If you are entertaining a preamp voltage drop (R39, 82K 3W is what I usually use) this would also be a good time to do it, but R39 can easily be replaced by jumpering the + ends of C20 & C21 with the required resistor.
Use carbon film/carbon comp for the plate resistors, metal oxide for screen grids & power supply dropper.
If you do attempt the work with the PCB installed & a component/leg drops out (R41 is the most likely cadidate) don't panic...there are usually alternative mounting points available, drop me a line in this case.
----------
www.myspace.com/markburness
http://www.facebook.com/markburness
|
bonedog569
734 posts
Dec 04, 2012
10:36 AM
|
I loosened up the board wihout removing it completely. I could gently turn it to expose enough of the underside to work on. A bit of a pain.
Next time I will practice my 'light touch' - lower heat soldering technique and try to avoid having to work on the underside. I did do a
few 'topside' replacements, -where the exposed leads where longer.
Getting the bias pot in is an essential mod IMO. Dialing the bias down is a big factor in getting the tone you are seeking.
Mark (5F6H) - is an invaluable resource, - but I'm afraid he will have little time to help you - he's already quite busy helping me climb out of all the holes I dig (or solder) myself into. ;)
----------
|
Rick Davis
966 posts
Dec 04, 2012
11:45 AM
|
Bonedog sez: "Getting the bias pot in is an essential mod IMO. Dialing the bias down is a big factor in getting the tone you are seeking."
Exactly right.
----------
-Rick Davis
The Blues Harp Amps Blog
|
528hemi
337 posts
Dec 04, 2012
2:12 PM
|
Mark,
Thank you for that advise. I will have a look and see how far I want to go right now. MIght do just the POT and the 2 resisters from the top.
I would have cut the resisters out and then tried to solder which would have been tougher
528hemi
|
Post a Message
|
