Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: billcreller on September 06, 2010, 10:21:39 pm
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A few years ago, I built two identical amps with a National (Valco mfg) circuit/schematic, with minor tube changes. One has always sounded excellent, and the other was trebly/tinny sounding. They were not built at the same time, but like almost a year apart. I decided to try and determine why one was good, and the other was crappy sounding.
After removing both from the cabinets, I noticed the the good one has a Hammond 1608 OT that I used in it, and the other has an OT that I had salvaged from an Alamo some years ago. Both the ones I built and the Alamo amp used 6V6s in PP. It's no surprise now that the Alamo was not a good sounding amp.
I wasn't aware that an OT could have such an effect on tone quality. I figured that if they matched the circuit requirements, all was well :smiley: Not true it seems.
Any opinions on this? Maybe it's like you get what you pay for. I'll have to get another Hammond........
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Oh geez, OT's can be of massive influence. I hotrodded a SF Princeton with the OT from a Dynaco 40 and the thing dramatically DOUBLED in volume and apparent power.
The guys at Mercury have probably gone religious fanatic over this, though I'm pretty sure they know what they're talking about. There's no question that you can choke off an amp's performance by using an inferior tranny. Now...whether the Mercury is worth twice the money as a Hammond? Dunno. A lot of research & trial and error has been done on transformers, the quality and magnetic characteristics of the steel used in the laminations, and lots of improvements (which you won't get if you use a salvaged 1956 tranny) have occurred since those days.
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I had a similar experience building a 5F2A 3yrs ago.
The amp sounded so lousy and did this decay thing where if you held a note in sustain instead of fading out it would abruptly stop.
I rebuilt that entire amp 3 times changing every part except trannies and sockets.
Turned out this cheesy OT a guy sold me on e-bay was for 70V speakers.
as luck would have it I found a MM OT for like $35 used on ebay and again lucky it was good.
That little amp sounded like it should after that, nice and gritty when dimed and sustained until momma got home.
Lesson learned, buy good trannys. no more salvaged stuff for me unless it's a throw together.
I buy heyboe,r hammond, magnetic components (preferred), or replacement parts if I'm building a clone. After all if I were cloning an Alamo it wouldn't sound like an Alamo with a MM tranny in it
Ray
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I think it depends on the source. I have used lots of "salvaged" transformers with great success. But, if you are salvaging a transformer from a company that made economy amplifiers and were cutting all possible corners, then you might get a substandard transformer.
Dave
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It might also be useful to know the primary impedance of the transformers in question. The lousy sounding OT from the Alamo was probably lousy sounding because it was low qualilty, but if it had a way different impedence than what you needed that might have contributed. I have an Alamo All American Five. Its is pretty crappy, but its got that distinctive Alamo sound.
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On the flip side, it's possible to have too "good" an output transformer for a particular amp. My 5F2-A build has undergone three incarnations, the latest using an "upgrade" OT from Allen Amps (forget exactly which one now). With a 10" speaker (Weber 10A100) and a Tweed Harvard sized cab, the bass is too clear and too pronounced for the amp. It needs the little OT it started out with to sound "right" to my ears. A little Tweed isn't supposed to have clean, strong bass IMHO.
I'm also under the impression that a lot of 5E3 Deluxe builders are frustrated by over-built output transformers. Part of "that sound" seems to be a moderately tortured OT.
Finally, Doug's transformers are every bit as good as Mercury Magnetics at way lower cost. Unless, of course, you get the 25-unit plus discount. They've got a damned good marketing/pricing strategy IMHO. Building two nearly identical Princeton Reverbs, I like the tone of the one I kept with Hoffman iron just as much as the one I sold with Mercury Magnetics iron.
YMMV
Chip
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On the flip side, it's possible to have too "good" an output transformer for a particular amp.
I've been wondering about this and what you say makes sense to me. It seems like going with very high quality units could lead to a "hi-fi" sound which is certainly not what I'm looking for in a guitar amplifier.
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The OT from the Alamo does look like a cost-cut item alright, but the old National amp that I used the schematic from has a small cheap looking OT also, and has great tone, and even has a field coil speaker to boot. Kinda hard to nail down the reasons some things work good while others suck.
The crappy sounding clone had a Princeton reverb circuit wedged in it, which I removed, thinking it was the reason for the lousy tone. It was likely OK.
Both of the clone types have Weber speakers of the same model also. Now I'm thinking about trying a different OT in my Princeton reverb clone, to see if any difference is apparent.
Thanks for all the replies....... :smiley:
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Your's being identical amps is a great test for this. It's about the only way to be sure.
Of course, it's all subjective. I have a pair of nearly identical highly modded BF Deluxe amps I built, one with a Mercury Mag OT and the other with a cheap Weber OT. Obviously, the Mercury example sounds great, however, the Weber version is the one everyone wants. You don't want crap parts but there does seem to be a point of deminishing returns. As always, it's a balancing act.
Dave