Tube Rectifier

thobbinghotrod · #1 08-24-2010, 02:38 PM

I tried to search, really.

I have a Fender Bantam Bass that I am trying to trade but before I do I want to make sure of what I have. I thought this amp sounded great but with only 25 or so watts it's not something a guy can take out of the house.

What does having a tube rectifier do for the sound? I hear the word sag all the time but this doesn't really mean much to me. Can someone give me an example, maybe a recording I can hear on youtube?

I may keep it for recording purposes.

Axtman · #2 08-24-2010, 02:52 PM

In a nutshell, when you hit a note (or chord) hard, the rectifier can't keep up with the power demand and the note (chord) gets compressed. While the note (chord) is tapering off the rectifier does not have to work as hard and can supply sufficient power.

On the other hand solid state rectifiers act instantaneously and don't have sag.

Tube rectifier amps have a certain amount of "squishness" as best I can explain it. Solid state rectifier amps are punchier.

toobalicious · #3 08-24-2010, 03:58 PM

love the tube rec in my B25B! i actually prefer my tone with that sort of compression over anything else ive done. its so musical--- there are no calculations being done! the compression starts way before audible distortion, even though technically, i guess they are one in the same (both are distortion due to overdriving).

thobbinghotrod · #4 08-24-2010, 04:09 PM

Well so far the trade guy hasn't called back so I get to keep the Bantam. I need to drag it out and get new tubes and have the caps looked at.

will33 · #5 08-24-2010, 05:42 PM

Folks say solid state rectifiers should be used on amps above 100 watts or so. I don't know exactly why that is but sag is pretty much what's been explained. "Voltage sag" or Power sag". The note gets a little compressed and then blooms out. Highly desired in guitar amps and I like it in low power bass amps as well. It's one of those reasons why folks say tube amps respond to the player better and are more "organic" for lack of a better term. The wide, wide world of valve jr. mods has a sag mod. Doesn't replace the ss with a tube but adds a resistor in the circuit to mimick sag. Vary the value of the resistor to get more or less sag. I don't know if this is workable with higher power amps or not. A maybe for those who really want it.

thobbinghotrod · #6 08-24-2010, 11:28 PM

I'm keeping the amp, I think I'll bring it to practice after I get it biased and checked out. We're also recording so I think I'll try it with the guitar as we're finding great sounds from unlikely sources, this will hopfully be another flavor to bring to the table.

will33 · #7 08-24-2010, 11:38 PM

If you're recording with it, that's definately another flavor to throw in there.

**line6man** · #8 08-24-2010, 11:42 PM

Thermionic diodes are known to have high forward voltage drops. This results in a lower voltage present at the anodes of all the other tubes, which causes them to push into overdrive a bit easier.

JimmyM · #9 08-24-2010, 11:46 PM

an amp like that would totally rock for recording purposes, and depending on what cab(s) you use with it, would make a nice amp for smaller gigs. but is there something wrong with the current tubes and caps? if it ain't broke, don't fix it.

thobbinghotrod · #10 08-25-2010, 02:47 AM

I took the tubes out and used them in a Bassman 10. I have a stack of old 6L6's but no real pairs, I have to get them tested and put a couple in.

T-Bird · #11 08-25-2010, 05:39 AM

Hi.

Tube rectifiers are usually quite modest powerwise, so they're found on lower power amps. There's a couple of examples of high power amps as well, and then there's two or more rectifier tubes to share the demand.

The sag is preferred by some guitar players, but there's nothing that prevents bass players from liking the dynamics as well

.

The best part of having a tube rectifier is that there's SS replacements for almost every rectifier tube so it's easy to compare the dynamics by simply swapping the SS module and the tube back and forth.

Regards
Sam

MAMMOTHvolume · #12 08-25-2010, 06:24 AM

Quote:

Originally Posted by T-Bird

Hi.

Tube rectifiers are usually quite modest powerwise, so they're found on lower power amps. There's a couple of examples of high power amps as well, and then there's two or more rectifier tubes to share the demand.

The sag is preferred by some guitar players, but there's nothing that prevents bass players from liking the dynamics as well

.

The best part of having a tube rectifier is that there's SS replacements for almost every rectifier tube so it's easy to compare the dynamics by simply swapping the SS module and the tube back and forth.

Regards
Sam

be careful doing this, you'll raise the voltage quite a bit so it could damage the valves in it.

Bassmec · #13 08-25-2010, 07:09 AM

Quote:

Originally Posted by MAMMOTHvolume

be careful doing this, you'll raise the voltage quite a bit so it could damage the valves in it.

This is the exposed arse of a good old 1968 Yorkshire Matamp.
gets quite enough Ht for 100 watts with a pair of 5u4g rectum-fires.

Of course you can just pull one out for some real greasy compressive Brimar EL34/Partridge transformer flavor!.
Oh err Missus thats good stuff!.

thobbinghotrod · #14 09-13-2010, 09:18 PM

I got the amp back from having the tubes biased. This thing goes lower than any amp I own, it still has the bassman sound but not as boxy.

I can't turn it up to any real volume but I'd sure like to record with it. I'll use it around the house mostly, I love this thing.

Destructobot · #15 09-14-2010, 12:30 AM

Quote:

Originally Posted by toobalicious

love the tube rec in my B25B! i actually prefer my tone with that sort of compression over anything else ive done. its so musical--- there are no calculations being done! the compression starts way before audible distortion, even though technically, i guess they are one in the same (both are distortion due to overdriving).

A SS rectifer doesn't make calculations either. It's just silicon instead of hot vacuum.

I had a '69 Sunn 1200s that had dual GZ-34's, the orignal GE's. That amp crushed in terms of tone, but came up a little short in the volume department. When it was cranked, the balance between fuzz and punch was all in the bass setting. I suppose I never played it through massive cabs though. It DID sound incredible for heavy guitar through two Marshall 4x12's

BassmanPaul · #16 09-14-2010, 12:02 PM

The difference between SS and vacuum rectifiers is mostly in the voltage drop. A tube will drop 50-75V across it. The more current the higher the drop. Thus as you play louder the B+ voltage drops leading to the compression so many guitarists crave. By comparison a SS rectifier drops less than one volt and that drop is static - it doesn't change. Dropping in a SS rectifier plug in into a tube socket increases the B+ by that 50-75V normally dropped by the tube. The power transformer also has the 5V heater load removed and the HV winding voltage will rise slightly. All this can lead to filter capacitor failure due to over-voltage and also the output tubes will be run harder. In amps that are inadequately designed you could even have a transformer failure.

Paul

panama · #17 09-14-2010, 12:06 PM

rec'tm? damn near killed em!

toobalicious · #18 09-14-2010, 12:24 PM

Quote:

Originally Posted by Destructobot

A SS rectifer doesn't make calculations either. It's just silicon instead of hot vacuum.

of course i do realize this... my statement was a generalization to include all variations of tone that i have experienced as a bass *player*, including some *very* expensive plug-ins.

BassmanPaul · #19 09-14-2010, 01:25 PM

Quote:

Originally Posted by panama

rec'tm? damn near killed em!

That is older than I am!

Paul