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M-Funf
09-06-2007, 01:50 PM
Last year, my FIL gave me his home made tube stereo setup. It was his college project. I've tried a couple of times to get this thing working, but I get lots of hum and don't have the expertise or time to figure it out. I replaced one of the missing tubes, but that's about all I've done.

Any of you know anything about this type of stuff? I don't know if it's worth anything, but I know that replacing the tubes would be some $. Should I just junk the chassis and sell the tubes and other major components by themselves?

I've got an amplifier, preamplifier, a Kenwood AM/FM stereo receiver (purchased component) and all the documentation to construct them...

Thoughts? Advice?

http://www.imagestation.com/picture/sraid225/pa6056428a535afc439379f27d8e2797e/e7d33361.jpg

http://www.imagestation.com/picture/sraid225/p91cc3e855c23a584e57b011c64d97aa4/e7d3334b.jpg

http://www.imagestation.com/picture/sraid225/pe73f4581045c45c6fa13a409a6742458/e7d33343.jpg

http://www.imagestation.com/picture/sraid225/pa084fe3addd7771330d54c7a251a9ed3/e7d33339.jpg

M-Funf
09-06-2007, 01:51 PM
http://www.imagestation.com/picture/sraid225/p2073f28ac588d2dbc8d198e5568cce31/e7d3332d.jpg

http://www.imagestation.com/picture/sraid225/p81b9d59e9035e6f1a510ca613bb4ac5f/e7d33326.jpg

http://www.imagestation.com/picture/sraid225/p5b8e405b0a538102da9bebaa45867e66/e7d33330.jpg

Maristar210
09-06-2007, 02:17 PM
Hello Jim N?

You out there?

BUMP

TMCNo1
09-06-2007, 02:17 PM
That thread title scared me a bit. I thought Toober Tom had invented something besides a boom box in a garbage bag there for a minute!

SkiDog
09-06-2007, 03:17 PM
Yea, I was with you on that one #1!;) :confused:

Toober Tom
09-06-2007, 03:23 PM
I must say I was thinking this might be about a mentod where I can tie the stereo cord around the tow strap while I toob. I have these for listening to disco while I ride my toob http://img.photobucket.com/albums/v240/Steves389/headphones.jpg

JimN
09-06-2007, 03:44 PM
I would guess that the preamp tubes are 12AT7, 12AX7 or 12AY7 and if it has a phase invertor, it's a 12AT7, or something like that. The outputs may be 6V6GT, EL34/6CA7, 6L6GC, 6550 if it's around 40W-50W, or 8550 if it's about 60W. They're easy to find and if you shop around, you can get good prices. Parts Express sells all of these numbers. I would stay away from high end shops or websites- they want an arm, la eg and small egg-shaped parts, usually the one on the left. Don't need to bother with NOS (New Old Stock) tubes, really. Just guy them in pairs (duets) or in sets of four (quartets). That way, they'll be somewhat matched. Mis-matched output tubes cause all kinds of biasing issues, which can show up as distortion and/or noise. If you want to buy tubes quickly, go to any good guitar store- most of these are still used in the better guitar amps, especially 6L6, EL34 and 6V6GT, with some still using 6550 and 8550, but less common. You should be able to get a pair of 6L6 for around $30.

Capacitors are another issue. They dry out over time and the hum is probably caused by the power supply filter caps. Remove the old ones and buy Sprague electrolytic caps. They're common and again, Parts Express should have them. It won't work with non-polarized caps, they need to have a mark for either positive or negative. Which is marked will depend on the brand- Sprague usually has a black stripe and a series of dashes, denoting negative. The large tube on the preamp is probably the rectifier, like a 5y3 or 5AR4 (more likely, based on the shape and size). If the heater coil lights up (it's the orange glow in the center of a tube) and you get sound, it's probably OK.

I doubt that the bypass caps are bad but if you replace the electrolytics and it still hums, you can check them out pretty easily by unsoldering one lead and checking for continuity in both directions. If you have that, they're bad. If it briefly shows continuity and goes to infinity, it should be OK. A good stereo shop may have a meter than can verify this for you.

If it was his college project, I would guess that he's an engineer or technician and used the most recent test equipment to build this set. If you get it back to spec, it should sound very nice. It might not be extremely powerful but if it has a pair of 6L6, EL34, 6CA7, 6550 or 8550 in the output stage, it'll definitely get up and go. If it has two pair/channel, it's probably 80W-100W/ch. If it has 6V6GT tubes, it may be less powerful but could also be a Class A design, which isn't as efficient but is really sweet and clean sounding. With those tubes, it could still be a Class AB with less output, too.

What are the model numbers?

Ric
09-06-2007, 03:45 PM
That tube right there is your problem. Head down to Sears and ask to use their tube tester.

JimN
09-06-2007, 03:47 PM
Ric- IIRC, Sears got out of testing tubes. I think he's going to have to go down to the Sylvania store, or maybe a Quasar dealer.

Is Curtis-Mathes still in business? Maybe a Heathkit or Olson Electronics store is still around.

Yeah, I'm that old.

Maristar210
09-06-2007, 03:53 PM
Ric- IIRC, Sears got out of testing tubes. I think he's going to have to go down to the Sylvania store, or maybe a Quasar dealer.

Is Curtis-Mathes still in business? Maybe a Heathkit or Olson Electronics store is still around.

Yeah, I'm that old.


Curtis Mathes. Wow a blast from the past.

I still have a quasar blender somewhere, wonder if it still works?

TMCNo1
09-06-2007, 04:05 PM
Curtis Mathes. Wow a blast from the past.

I still have a quasar blender somewhere, wonder if it still works?
I bet that was a hoot, watching the Brady Bunch on the blender!
It had to beat sitting around watching the radio!:rolleyes: :D

M-Funf
09-06-2007, 04:06 PM
WOW, Jim...thanks for all the info.

I don't know that I want to try and resurrect this thing (I'm a mechanical engineer...electrons elude me).

I'm not sure about all the tubes, but I know that the one I replaced was an RCA 6973:

http://us.st11.yimg.com/us.st.yimg.com/I/triodeel_1965_3875346

There are also two Sylvania 7199's:

http://i15.ebayimg.com/05/i/000/af/00/5784_12.JPG

and 4 12AU7's on the preamp:
http://i2.ebayimg.com/07/i/000/95/92/93a4_3.JPG

I'll take a look at the schematics and write down the model numbers on the tubes.

Upper Michigan Prostar190
09-06-2007, 04:16 PM
Jim, your way more of a guru on this stuff than I am, so I have to ask a dumb question, why would that need a phase invertor? I have seen amps that use 12AX7 or a 12AT7 for a phase invertor. I think my Laney AOR 30 uses a 12AX7 for a phase invertor for hte reverb, I THINK..... again, I am not a guru on this stuff. I wonder if you can buy those old tube testers anymore?? ebay?? how would you ship the beast though....!!!! :eek3: I know Mesa used to build Baron Tube amps for home stereos a while back in the 80's & 90's and they were VERY expensive, aimed at "serious audiophiles".......I have always wondered how good they sound coupled with some awesome speakers.

Leroy
09-06-2007, 04:31 PM
Great for your FIL! What are you going to do with it once you fix it? You really going to use it?

Heathkit! My first rig in amateur radio!

I would say Jim is right on and think it is likely dried out caps. You can always tack on a cap in parallel with another cap to see if that fixes it. Remember there is voltage in there that can cause damage.

Maristar210
09-06-2007, 04:31 PM
Jim, your way more of a guru on this stuff than I am, so I have to ask a dumb question, why would that need a phase invertor? I have seen amps that use 12AX7 or a 12AT7 for a phase invertor. I think my Laney AOR 30 uses a 12AX7 for a phase invertor for hte reverb, I THINK..... again, I am not a guru on this stuff. I wonder if you can buy those old tube testers anymore?? ebay?? how would you ship the beast though....!!!! :eek3: I know Mesa used to build Baron Tube amps for home stereos a while back in the 80's & 90's and they were VERY expensive, aimed at "serious audiophiles".......I have always wondered how good they sound coupled with some awesome speakers.


UMP did you just have a worthwhile post? :D :cool:

Upper Michigan Prostar190
09-06-2007, 04:36 PM
Also remember that those caps can potentially kill you. in most amps, they store one helluva charge and if your not careful, you can be electricuted. I had to trouble shoot an amp of mine once while it was live to solve a reverb issue. I had the customer support guy on the phone, and he told me to wear rubber sole shoes, rubber gloves, and put one hand behind my back and only touch the amp chassis with ONE hand, and keep the other hand in my back pocket. I did just fine, no problems. BE CAREFUL! those caps can hold a charge for a while even when not powered up. You can dissipated the charge with a lead and a resistor shorted to ground if you know what your doing. then its typically safe. I am sure Leroy & Jim know more about this.

Upper Michigan Prostar190
09-06-2007, 04:37 PM
UMP did you just have a worthwhile post? :D :cool:
I believe so. I think its #37 if I am not mistaken.

M-Funf
09-06-2007, 04:45 PM
Also remember that those caps can potentially kill you. in most amps, they store one helluva charge and if your not careful, you can be electricuted.

See, this is EXACTLY why I want to get this thing out of my shop! :shocked:

Leroy, my plan is to sell/trade this on craigslist. I don't have the time for it, really.

I have another Tube amplifier/stereo with speakers that I'm going to build an enclosure for soon. I'll try to get some pictures of that and post them as well. It's a very nice unit with large speakers, an old turntable, and great warm sound

Upper Michigan Prostar190
09-06-2007, 04:59 PM
Its funny......the whole world is trying to make electronics smaller, except guitar/bass amps. Us tonal discriminating elistist bastages will just not accept anything less than a tube amp for tone. They have been trying to replicate that with solid state electronics for well over 20 years, and it just dont work. Line 6 PODs, Digitech, Johnson, all those claim to nail the tube tone, in the end, its just warmed over dog crap. you just cant beat tube tone. They are heavy, cumbersome beasts, but there is nothing that sounds like them. Vintage keyboard players go through the same thing with the old Leslies.

M-Funf
09-06-2007, 05:09 PM
There's NOTHING like the sound of a Hammond B3 with Leslie sound :love: :love:

Ric
09-06-2007, 06:02 PM
There's NOTHING like the sound of a Hammond B3 with Leslie sound :love: :love: That's what I always say

JimN
09-06-2007, 06:23 PM
Jim, your way more of a guru on this stuff than I am, so I have to ask a dumb question, why would that need a phase invertor? I have seen amps that use 12AX7 or a 12AT7 for a phase invertor. I think my Laney AOR 30 uses a 12AX7 for a phase invertor for hte reverb, I THINK..... again, I am not a guru on this stuff. I wonder if you can buy those old tube testers anymore?? ebay?? how would you ship the beast though....!!!! :eek3: I know Mesa used to build Baron Tube amps for home stereos a while back in the 80's & 90's and they were VERY expensive, aimed at "serious audiophiles".......I have always wondered how good they sound coupled with some awesome speakers.

If there's a single output tube, it has to deal with the whole waveform of the signal (think sine wave). Since the voltage can't go below zero, they raise the mid-point of the signal to a point that will allow the negative phase to go to the maximum of the power output without clipping and isolate the output from the speakers with a transformer. The raising of the signal is through a DC bias voltage and we all know that speakers really don't like DC.

When an amp has one or more pairs of tubes, one of each pair will handle either the positive or the negative phase. The signal needs to be inverted, since the tube circuits are identical and again, the signal can't go below zero, so they invert one half and the minimum signal level is zero volts. There's always some delay when a signal goes through a circuit and the phase invertor is no different, so there's always a little bit of a step where the two halves of the wave meet. The bias control helps remove any hum from an imbalance between the two halves and if the circuit is well designed, the notch will be minimal.

The great thing about tube amps is that they have tons of voltage at their disposal, which means they can provide a lot of gain. The transformers limit their drive current, but depending on the design, that can be less of a problem. This is one reason they aren't used for driving subwoofers.

The 12AX7 is probably a driver for the reverb. The 12AT/AU7 doesn't need to provide as much gain like the 12AX7, if it even needs to provide any.

Tube checkers are OK for checking the gain of some tubes but useless for checking for microphonics. Output tubes are checked and matched fairly closely but, according to a friend who designs, builds and repairs guitar amps, preamp tubes are checked for microphonics and that's about all. He has been working on a jig for testing them for maximum consistency and he decided to build it after seeing such a wild variation if the tubes he buys, even though he buys them by the case.

I'm sure Don Randall (Mesa Boogie) built a lot of things for friends and then started selling the Baron amps after the reputation got out, but it was very limited distribution.

Googling vacuum tubes will show thousands of hits and one good use of these is to find alternative tubes when one isn't available. Parts Express is where I generally buy my tubes and their prices are pretty good. I recently bought some JJ brand tubes for my stereo amp, and they were known as Tesla, previously. They're Czech made, very nice and very consistent. The tubes for the amp in my avatar came from there, too.

JimN
09-06-2007, 06:27 PM
There's NOTHING like the sound of a Hammond B3 with Leslie sound :love: :love:

I remember when Yamaha came out with the DX-7, in the early-mid '80s, and it had thousands of sounds, all kind of thin. There's nothing, NOTHING like the sound of a Leslie speaker. Listen to Joe Walsh's guitar on a lot of his records. That's not a Uni-Vibe or any other pedal. Coupled with a B3 it doesn't get any better, even after all these years.

M-Funf
09-06-2007, 06:29 PM
I'm sure Don Randall (Mesa Boogie) built a lot of things for friends and then started selling the Baron amps after the reputation got out, but it was very limited distribution.

Maybe I should take a drive over to Mesa Boogie and talk with Don Randall...see if he wants all this stuff...He's just across town from me.

JimN
09-06-2007, 06:39 PM
Its funny......the whole world is trying to make electronics smaller, except guitar/bass amps. Us tonal discriminating elistist bastages will just not accept anything less than a tube amp for tone. They have been trying to replicate that with solid state electronics for well over 20 years, and it just dont work. Line 6 PODs, Digitech, Johnson, all those claim to nail the tube tone, in the end, its just warmed over dog crap. you just cant beat tube tone. They are heavy, cumbersome beasts, but there is nothing that sounds like them. Vintage keyboard players go through the same thing with the old Leslies.


The first transistors distorted so badly, it became an actual sound, used by Dallas/Arbiter, known for its round Fuzz Face distortion box. There were others around the same time and they were noisy, nasty, temperamental, usually lame and never came close to the sound they were trying to replicate. Then, probably by accident, they found that they could create enough harmonic distortion that the octave of the original note came out and it was just about as loud, too. That became a highly popular effect, as well as all of the others that Les Paul thought up, like flanging (accidental), phase shifters, multi-tracking, delays and others that go back to the beginning when he jammed the needle from his mother's phonograph into his guitar.

Another thing that plays a big part in how things sound is the actual proximity and orientation of one circuit to other circuits and how they're wired. Fender had so many requests for their old, classic, amps and they made them with printed circuit boards, like most other equipment. Sure, people had a '59 Bassman but the old ones were on phenolic paper with brass eyelets hand-wired, point-to-point, with cloth covered wire and instead of being in nice parallel rows on a PC board, the wires were bent and ran along the corners of the chassis. Big difference in sound, when you compare an original with the reissue.

JimN
09-06-2007, 06:51 PM
Maybe I should take a drive over to Mesa Boogie and talk with Don Randall...see if he wants all this stuff...He's just across town from me.

Sorry, I was wrong. It was Randall Smith who started Mesa Boogie.

If you get it running well, try it out. You may not like the way it looks but you'll probably like the way it sounds. If you sell it, get a lot. I would probably hold onto it since it was built by your Grand Father.

M-Funf
09-06-2007, 06:58 PM
Sorry, I was wrong. It was Randall Smith who started Mesa Boogie.

If you get it running well, try it out. You may not like the way it looks but you'll probably like the way it sounds. If you sell it, get a lot. I would probably hold onto it since it was built by your Grand Father.

Dangit...now I have to keep it, don't I...If I end up gettin' 'lectrified I'm blaming all y'all 8p

Maybe I'll find someone who will help me diagnose it and see if we can get it going.

JimN
09-06-2007, 07:24 PM
Like I said before, if the power supply capacitors are replaced, the hum should go away. Just make sure to observe the correct polarity. Any tube that looks fogged on the inside needs to be replaced. The rest should be OK.

Upper Michigan Prostar190
09-06-2007, 07:38 PM
There's NOTHING like the sound of a Hammond B3 with Leslie sound :love: :love:
Tru dat. :toast:

Footin
09-06-2007, 07:45 PM
Remember Heathkit?

M-Funf
09-06-2007, 07:54 PM
If you sell it, get a lot. I would probably hold onto it since it was built by your Grand Father.

It was built by my "FIL"... Father in Law. He gave it to me to see if I could fix it (heck, he's the electrician!!!).

He said I could sell it if I wanted to as I have so many other projects, but I have NO idea what I should ask for it. I looked up the tubes, and they came up to a total of about $300. But since I don't know if they're any good (except that they don't have any haze on the inside, they glow, and they get warm), and I don't know much about the Inductor or X-Frmr's, I have NO idea how much to ask for!

Upper Michigan Prostar190
09-06-2007, 08:13 PM
Sorry, I was wrong. It was Randall Smith who started Mesa Boogie.

If you get it running well, try it out. You may not like the way it looks but you'll probably like the way it sounds. If you sell it, get a lot. I would probably hold onto it since it was built by your Grand Father.
Yes sir, Randall Smith is him. He even signed the inside of my amp chassis for me. I had one of the first Road Kings, and it had an over heat issue due to no cooling fan. Elusive issues, had to be sent to Mesa. Randall got involved in the repair of it himself and installed the cooling fan. Randall felt bad so he gave me a full set of tubes, and some freebies, and he signed the chassis. Kinda cool. :cool:

JimN
09-06-2007, 08:50 PM
If the pre and power amps are from kits, sold by Kenwood, like the tuner, ebay is where I would sell them, or www.audiogon.com

They may be able to help to determine a value, too.

The caps should be $25, more or less, depending on the capacitance and voltage. Start there. It may need nothing else. Just being old is no reason to replace all of the tubes. Remember my comments about repairing boats using the "shotgun method"? It applies in everything. The fact that they're kind of old means one thing- they're kind of old. If something goes bad, it's likely to be the power supply caps, followed by the plate or grid resistors, followed by one or more tubes. If a tube turns into a lightbulb, the tube socket will probably need replacing but that's about a $5 part. The only parts that are really expensive are the transformers and they don't go bad unless there's a good reason.

Ask your F.I.L.- he'll probably agree. Start small, see if it works and see what happens. BTW- clean the controls and switches. The tube sockets will be cleaned just by inserting the tubes repeatedly.