Topic: Anybody here have any experience with fixing Ampeg tube amplifiers?

[Frankencake]

i would almost give up my suzuki titan for a set of machintosh tube amps.  i have a pair of 30 year old bose 601's that would work REAL nice with em.

Nothing is too expensive for a pipe dream:
http://cgi.ebay.com/HERNIA-WARNING!-McIntosh-MC2102-Tube-Amplifier-100-wpc!_W0QQitemZ300282116224QQcmdZViewItem

[fuzzybutt]

thats about 5x the book value on my car  i had no idea that stuff had gotten so expensive.

[TwoTired]

I just noticed this thread.

Running the PT with only half the primary windings, reduces it's power transfer capability from the primary to secondary by about half.  Certainly the turns ratio has been effected.  I would expect the voltage output would be lower and will sag quite a bit upon approaching rated load.  The transformer core saturation can't be maintained when full power is being demanded from it.

It will still "work", but the voltage and bias changes during power demands will add to the distortion of signal throughput.  Guitarists may actually like the sound.  It should certainly "break up" at lower volume settings than with both primary windings being properly driven.

You may also find little difference in volume settings above a certain point, only more distortion, given a constant signal input.

A little searching, uncovered that it was a 120 watt output amp.  That's large venue power, IMO.  With half the primary working you can expect 60 Watts output, I'd guess, likely with some distortion.  If you like the distortion, it could be a small club amp or a practice amp.

Ampegs used to be a popular bass amps, able to deliver clean clear bass at high volumes, and move large speaker cones, too.

Kustom amps were quite popular in the very early seventies, all transistor.  I still have my Kustom 100 with 4 - 10s in it, bought in 69 or 70.  I also have high frequency hearing loss.   I could play outdoor auditoriums with it.  Which was about the only time I could get it to add character to the signal input.  It was soo sweet.  But, I said "huh" and "what" a lot for three days afterward.  I have a CBS Fender Twin w/2 JBL 12's that didn't help my hearing any, either.

Cheers,

[Frankencake]

I just noticed this thread.

Running the PT with only half the primary windings, reduces it's power transfer capability from the primary to secondary by about half.  Certainly the turns ratio has been effected.  I would expect the voltage output would be lower and will sag quite a bit upon approaching rated load.  The transformer core saturation can't be maintained when full power is being demanded from it.

It will still "work", but the voltage and bias changes during power demands will add to the distortion of signal throughput.  Guitarists may actually like the sound.  It should certainly "break up" at lower volume settings than with both primary windings being properly driven.

You may also find little difference in volume settings above a certain point, only more distortion, given a constant signal input.

A little searching, uncovered that it was a 120 watt output amp.  That's large venue power, IMO.  With half the primary working you can expect 60 Watts output, I'd guess, likely with some distortion.  If you like the distortion, it could be a small club amp or a practice amp.

Ampegs used to be a popular bass amps, able to deliver clean clear bass at high volumes, and move large speaker cones, too.

Kustom amps were quite popular in the very early seventies, all transistor.  I still have my Kustom 100 with 4 - 10s in it, bought in 69 or 70.  I also have high frequency hearing loss.   I could play outdoor auditoriums with it.  Which was about the only time I could get it to add character to the signal input.  It was soo sweet.  But, I said "huh" and "what" a lot for three days afterward.  I have a CBS Fender Twin w/2 JBL 12's that didn't help my hearing any, either.
Cheers,

I was kind of waiting for you, TT, to show up and chime in.  I am thinking the same thing you have stated here.  But the proof is in the pudding.  The amp still has tons of headroom before it distorts and B+ voltage is right where it should be.  To be honest, I haven't heard it distort yet until I over drive the midrange section.  There is a triple triode 6k11 with a section driving the midrange only (Weird but cool at the same time) and cranking the midrange pot overdrives that triode, making for a beautiful crunch.  I have pushed the amp with the halved PT and it seems to not break up.  My theory is that the capacity of the pt is so over the top with two primary windings and one will do.  I have to get a more appropriately rated speaker before I can make a definite call on the weakness or strength of the pt.  Right now my cones in my Super Reverb are rattling before the signal does.  I think that Ampeg just made a ridiculously strong PT.  It will be an interesting exchange when I buy a new PT.  If there is a drastic difference I could make it a switchable function.  I can protect both windings with fuses and have two switches controlling line voltage to each winding.
By the way,  someone told me a long time ago that the frequency that you hear when your ears are ringing is the one that you won't be hearing for long.  I get it around 2.5khz-3khz.  3khz+/- is the pitch of a babies crying and humans are tuned to that frequency.  I never liked that sound so I won't miss it. 
Bass tonality character is difficult to achieve with such a large cabinet.  I think that the best is to have two audio sources when playing live.  One of them should be right in your face and small and the big one should be for everyone else.  the usual compromise is to use a four ten w/a horn on top of a single 15".  This lets yo get a picture of the high frequencies that show up later  Bass, especially, has to travel quite some distance before it "develops" in to it's tone.  It also needs space to mellow and shape itself.
My pet peave is when a guitarist plays with his amp pointing at his knees.  You can't hear the high frequencies when you do that and then the guitarist ends up turning up and up and up. Speaking of fender twins, it's been more than one occasion, as a sound engineer, that I have had my ears blown by some knucklehead pointing his amp this way and it happens to be pointed at my face 40 or 50 feet away.  The high frequencies drive right through my skull and he thinks his guitar sounds "sweet".  Fender twins are notorious for their faithful reproductions of highs and pair that directional positioning with a Stratocaster's bridge pickup and you can ultra-sonically clean your occipital lobe. 
I had an argument with a 30 year veteran blues musician about this very thing.  At the end of the might I had no hearing left and was blind in my ears for three days.  I swore that I would avoid his gigs like the plague.  One gig a few years later, we once again met.  This time he put his amp on a chair and pointed it at his head.  It actually sounded good that time since he could hear what his tone was and the stage volume was palatable.
Ok. I am ranting like an old burnt-out roadie.  "I had to beat them to death with their own shoes and choke them with the brown M&M's"-------SS

[TwoTired]

A guitar string attack has a sharp rising edge.  This is when the PT core saturation is needed the most.  Having half the input winding will not restore the core saturation as quickly for the next attack depending how close that next attack is to the preceding one.  So, what you hear is going to be related to the signal source you provide.  I always used to use a signal generator and a dummy load to monitor the amp and find where the distortion begins.  The percussive attack of a guitar string just doesn't have what it takes to verify a clean amplified signal.
If you don't care about signal throughput purity at full output power, then it is easy to understand why you think the PT now works as well when half of it is disabled.  I don't believe it was over designed at all, provided you test to the full original specifications. Clean 120 watt amps were not that easy to make in the 60s and 70s. (think PA use where you do NOT want to color the vocal sound texture.)
Guitarists, on the other hand WANTED that amplifier and speaker coloration added to the sound source signal from their guitar.  It gave the guitar sound new life.  I don't recall any of the Ampegs being popular with guitarists because they were so clean. (except maybe Jazz or country guitarists.)  But, that was the very reason why bassists liked it.  Clean power at full output.

The pre CBS/Pre 68 fender twins actually colored the guitar signal.  When the CBS engineers took over, they came from an audiophile background where amplifiers were NEVER intended to color the signal source sound.  Many believe that CBS ruined the fender amps, by making them SOO clean that they had no "tone" or added no life to the sound throughput at all, unless you pushed them to 90% output power, which is damned loud.  In the those days pre-effects weren't quite as prevalent, and those that were available didn't have much dynamic range for throughput, in other words, they changed to guitar signal, even when bypassed.  When engaged, the guitar harmonics were corrupted or lost, and the tone that the amp normally added was changed.
My CBS twin is great for vocals, if you use it just for that.  O any other clean signal you wish to reproduce at a louder level. Nowadays, if you have pre-effects, the sound from those is accurately reproduced with a nice clean throughput amp.
BTW, my Fender twin has tilt back legs for that in-your-face sound projection.  But, I've learned to use earplugs with that amp.

Anyway, while the plate voltage may meet spec with no signal input or throughput, the loss of pt core saturation will cause it to sag at some point below the peak rated output of the amp.  Those tubes need the most power when pushed hard and that power comes from the PT core.  I also wonder how you are measuring the B+.   With a Oscope?  If a meter, what is the frequency response of the meter?  Alternately, over what period does it sample the average voltage?

In those day when this amp was available, audiophiles would use very powerful amps, and then only use 10% of the output power capability.  The reasoning was that the frequency response curve was not linear through the entire power available range, but it would remain linear when using a very small part of that total range, giving clean, quiet, accurate reproduction of all frequencies throughput.  I will freely admit not ever encountering this particular VT-22 amp.  Maybe they put that triode section in to get the guitarist desired "tone".  But, I would expect they didn't want the final amp section to add "tone", and that's where the power hog lives in that amp, and why the PT is designed as it is.  You push the power amp and deplete the PT core saturation, and the B+ will sag changing the bias stability on the all the tubes.  But, as I said, you might just like the tone changes that this adds.  I remember when Fuzz boxes were popular, changing sine waves to square waves, and then letting the amp color the harmonics produced.

There were many guitarists who wanted the amps to color the sound.  Off Biasing the amps was one such method.  You can get the sound to color in the various stages of the amp, preamp on through power amp sections.

Do you have access to a THD HotPlate Power Attenuator?  Or, some other output attenuator that allows driving the power amps to full spec independent of speaker load?

See: http://amptone.com/

Just to brag a bit, I also own a '55 Fender  5E8 twin amp.  It's 50 Watt and plenty loud for clubs.

Cheers,
 

[fuzzybutt]

i had a pre-cbs bandmaster years ago, lost it in a house fire. best amp i ever had.

[Frankencake]

TT, I so want to sit and have a chat with you of all things electronic.  You see, I consider myself an amateur in this realm.  My O-scope died a few years ago and while attempting to fix it, I took either 750 or 1050vdc across my shoulders.  When I could finally see again, (few tenths of a second) I was standing up the O-scope was on the floor about ten feet away.
  I gave up on that particular project and gave it to a buddy who need one of the same models for parts.  I haven't needed a scope since then but I have been looking in the past week for a reasonable one on Ebay.  I don't have a signal generator but I substitute a keyboard that has a perfect sine wave as one of the sounds.  The folks at Casio tend to take the easy way out and call it a tin whistle or something.  I hear your case about core saturation and fully agree that it may be the case.  I am using, at the absolute most, 20% of the available power of this amp.  So it will not be an issue.  Incidentally, the peak available power from a 7027 tube is about 35 watts.  It is possible to make these amps put out 140 watts at the risk of a small fire.
  When I get a new scope, I'll run a battery of tests and record the results.  I found a used original PT from a V4 guy for 100 clams, but I am reserving the next few bucks for the powder coater. (this is still a bike forum and I am still building my cafe)  For now, it will be a good living room amp until she gets tired of the amp showroom and it goes back down stairs.  I have, in my living room, my entrire collection of amps.  They are nothing special like '55 but they are paid for.  I have a CBS '76 Twin Reverb that I got for $50.  A '68 Super Reverb which has an  unmolested-by-CBS blackface circuit that I got for free and the largest combination amp Fender ever made, A 1972 Fender Super Six Reverb.  I few year ago I started getting more serious about the amp tinkering thing and while researching, I learned about the Super Six.  It is the same head as the Twin giving it 100 watts but it has six ten inch speakers with a two ohm load.  I had to have one since they will never make anything like it again.  I found one in someones basement and bought it.  After all of the glory of the immensity wears off, at the end of the day it sounds absolutely great.  I've always been a fan of 10" speakers anyway.  It is a great living room amp, especially with the twin perched on top.  It really is just stupid and over the top obnoxiously big.  I had to have one.  I view it as an investment.  Look it up, they really are neat and dumb at the same time.  Totally ineffective unless you are 15 feet away or it is pointed at your head.  They don't have legs but it does have wheels. 

Getting back to the PT.  Try this question:  Wouldn't the lack of core saturation be almost to the same effect as using a vaccum rectifier tube and cause the same type of sag?  In effect having a saggy power supply would, to some point, mimic a saggy 5u4g perhaps?  Would AC sag be the same as DC sag and have the same effect?

And yes I even said to that old blues guy that his amp had legs and he should use them.  He looked at me like I had two heads....

I do not have a hot plate.  I was thinking of making one but I haven't gotten to that point yet.  I may call an old amp guru buddy and ask him if he wants to experiment with me on this Ampeg the next time I get to NY.  I really am curious if the modified PT will have a drastic effect at high power.  We shall see.  For now, come to think of it, I have to buy a good matched quad of 7027's.  The tubes that are present are from two different manufacturers and I'm sure that they are beat up.  One set was redplating when the OT was blown so they have to be close to toast.  If I did everything to this amp that I would want to do, it would be close to the asking price of another one.  For now, it'll have to do.  I gotta finish my bike!!!!!!! 

i had a pre-cbs bandmaster years ago, lost it in a house fire. best amp i ever had.

I dropped off a bunch of stuff at the salvation army a while back.  I walked in the back room and there was a beautiful bandmaster just sitting among kid toys and dirty clothes.  I asked how much they wanted and the guy said that there were no sales done out of the back room.  Yeah right, I said.  I went back that afternoon and the next day but it never showed up.  No sales my a**

[Retro Rocket]

Hi guys,

Do you have access to a THD HotPlate Power Attenuator?

There's now a much better way to achieve good tone at lower volume, check this out, its called "Power scaling".

http://www.londonpower.com/pskinfo.htm

and a demo....go to the end of the clip to see the power scaling.

Mick

[fuzzybutt]

hmmmmmmmmm thats a hot sounding 18 watts, me likey me likey

[Frankencake]

It's a good thing that I have my headphones on this late at night.  Nice amp and good idea but taking the volume out of tone is what's wrong with this country!

[fuzzybutt]

thats an expensive damned 18 watts too. $1750.00 to $1900.00 between the sellers i found online. think i'll just stick with my little fender champion 30.

[Jonesy]

Good point about the wattage. You're running a 100+ watt amp, whereas my "Maggot-Box" is only running around 35 watts or so per channel. It may be primitive by today's standards, but the tone quality and depth us like nothing else I've ever heard.

I have seen plug-in replacements for the 5U4, etc rectifier tubes that can convert them to solid state. Only thing is you have to go back and re-bias the driver tubes as you don't have the voltage drop across the 5U4 plates anymore.

This "Maggot-box" you are talking about is a stereo amp?  I've often tried to find a junk one of those as they are out there just like old Hondas.  I'd like to see the look on my girls face when I come upstairs with that.  "Move over Sony, Here comes old tech!"  And I have the power to rebuild them!!!  Boowhoohaha!

I know this thread is about guitar amps, but since you asked... (no hijack intended).

A few pics:


The tuner and phono (taken while I had it apart for refurbishment):





It's a late-50's Stereophonic "Magnificent Magnavox" with a Collaro turntable and 196-10 Amp





It has 2 side-mounted 12" Woofers and 4 6" forward tweeters. A buddy who's into that kinda stuff commented, "Can you imagine how that thing would sound with modern speakers with heavier magnets?" I dunno.. it sounds pretty damn good with the originals!

[azuredesign]

My experience with Ampeg is limited to a early 60's Reverbrocket that I was never able to coax enough gain out of. I ditched the 7591 output tubes and changed to a deluxe reverb output transformer, and used 6v6's, but it was still not my cup of tea.
I like the idea of keeping the primary voltage high but varying the secondary.   When it's done with the output transformer, is that power scaling?
 

I had a very good result with a Gibson Discoverer several years ago. That used el84's( a friend gave me a pair of Telefunken tubes he'd found at the dump) and had the most harmonically rich break up I've ever heard. Wonderful amp to record with.

If it's a reasonable analogy to think about amp headroom as similar to engine torque, and loudness, whether distorted or clean as horsepower, then I'm a cruiser guy that likes to crank it every once in a while.

As an aside and FWIW, I also think ear protection is a good thing for young players, as I am also pretty deaf at this point as well. Custom made ear plugs are pretty comfortable, and allow interchangeable filters to reduce sound pressure to varying degrees while maintaining more of the higher frequencies.

[Frankencake]

Jonesy, I'm only 38 years old but I remember from way back in my childhood, when everyone was throwing those things out.  It's funny how all of that old tech is still sought after and actually sounds good.  When I was a kid, my aunt would listen to Polka records on a tube amplified turntable.  She probably still has it.  I also remember having to "wait" for machines to warm up.
 All of that old tube stuff would actually survive a EMP from a nuclear bomb, unlike modern electronics.  One of my old tech gurus actually would remove the transformers and put the whole rest of the amp in to the dishwasher.  That is if they didn't have any cardboard capacitors but still, even if you wave a cellphone at a puddle you need a new one and all of your stored information is lost

MAs an aside and FWIW, I also think ear protection is a good thing for young players, as I am also pretty deaf at this point as well. Custom made ear plugs are pretty comfortable, and allow interchangeable filters to reduce sound pressure to varying degrees while maintaining more of the higher frequencies.

.

I still take my earplugs every time I go out to a bar much less a band gig.  I even use them when I vacuum the floor.  I make a little bit of money with my ears.  I'd kinda like to keep them.