Something Glowing This Way Comes

General discussion for all questions based in the home audio/video world.
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Mike S.
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Postby Mike S. » Sat Jun 24, 2006 3:52 pm

westend wrote:Now that is what I wanted to hear. I've been studying a little on tube circuits but that "crack habit" with the associated compulsive scroungophiling behavior sounds like it's right up my alley. I've been on a recent binge on the SS stuff (coke habit?) and at present have five pieces of gear in various states of transit. Your post and the look of Jim's amps have given me some inspiration. I have the efficient speakers-Fostex BLH at 93db. Is there a particular direction to start or one piece of gear to start with? I have SS tuners and amps but no straight preamp other than using a SS receiver. Would a tube amp be the place to start and what circuit is recommended?



Well if your into the Yard/Garage/Thrift Store scrounging thing, it's a good place to start finding vintage tube gear on the cheap.
Ham radio meets are another way to find related gear. Craiglist, eBay.......of course, caveat emptor with eBay......

Don't expect to pay big bucks for the stuff, set a budget. I go as cheap as possible, like free. :cwm20:
Be patient. Unless you absolutely have to have it, the deals will come with time.
If you can get it dirt cheap, grab it whether if works or not. Say if you pick up a non-working tube amp for a couple bucks, the iron and tubes are worth that.......organ amps are also a great source of tubes and iron for projects.

Old vintage tube console stereos can be had for peanuts, but do keep in mind most of them have small output transformers and are a little thin on bass. But if they can be had for a few bucks, why not? You can always make up the difference with a subwoofer if need be. Besides, parts is parts.....
And if you come across test gear for cheap, nab it. A good old school volt/ohm meter is a good thing to have, or a vacuum tube volt meter, or a tube tester....etc......you start working on the circuits, you'll have to measure voltages, do some math, test tubes...etc...
I still need a good volt/ohm meter, but I do have a good bench DMM. It's good to have both.....hell, you can get obsessed with the test gear as well......eventually, you'll want a scope if you don't have one.

You mention you have solid state power amplifiers, maybe build a simple tube linestage and use it before a power amp. Kinda best of both worlds, SS bass grunt with tube flavor.
I see kit linestages for ok prices, and I suppose for ease of build they are ok deals, but I encourage DIY as in scratch build because you can do it for damn near nothing.

Hear is a few links to uncle Ned's tube data page off the website. On page one of the RCA resistance coupling charts, explains how a tube is loaded, the break point frequency between stages, etc...
http://www.triodeel.com/rca_p1.gif
http://www.triodeel.com/rca_p2.gif
http://www.triodeel.com/rca_p3.gif

Look at that diagram no. 1. on page 1. You build a power supply for the tube's plate, a filament winding or transformer for the heaters.
You park a volume pot (100K, usually) in front of the tube feeding the grid. The cathode resistor and bypass cap sets the bias and gain of the tube, with the trick of getting the tube working in it's linear region of it's curves. Grid voltage as well.
The coupling cap from the plate to the next stage can either be another tube stage or a power tube for a single-ended amp, or a phase inverter circuit for a push-pull amp.
Or you can hook the coupling cap to a pair of RCA jacks and make it a linestage.
I think the break point frequency is explained in that link to pg 1.

Linestages and pre-amp circuits can get WAY complicated than that, but that's about as simple as it gets.

I started with a couple Eico HF-12 integrated PP 6BQ5 mono amps to cut my teeth with vacuum tube circuits. A simple tube amp is a fine place to start, it's all a matter of checking parts for tolerance, tubes, voltages. It gets easy over time, just don't get tagged......take heed to the high voltage.

As far as what circuits are recommended, you may like a single-ended tube amp circuit or you may think they suck and prefer a push-pull. You may think push-pull sounds like clean solid state, (not a bad thing) and prefer a bit more colored sound of a single ended directly heated triode amp. It's all a matter of finding out........

Recommended circuits to build? Start off easy. Rebuild a simple console tube amp and get the hang of things, then move on to a scratch built circuit/amp.



What's wrong Jim, a little miffed by the crack habit comment?
You have a pair of 8, 10 watt SET monoblocks with intentions (I think) of building a linestage or pre-amp. You think your just gonna stop after that? :)

Mod those Forte xovers......trust me.....
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westend
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Postby westend » Sun Jun 25, 2006 2:04 am

Thanks Mike, I'll take your advice and start with the simpler stuff. I don't think I'm ready for a scratch build. More a lack of time than a lack of flux. Do you think a Fluke true RMS will get me through a bit of testing or is a scope mandatory?
Pioneer 860, Soundstream 600-4, Directed 1100d, CDT IEK, CDT EF61CF, 2-IDQ-10's NoGOT-No gas on Thurs.




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Mike S.
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Postby Mike S. » Sun Jun 25, 2006 9:40 pm

westend wrote:Thanks Mike, I'll take your advice and start with the simpler stuff. I don't think I'm ready for a scratch build. More a lack of time than a lack of flux. Do you think a Fluke true RMS will get me through a bit of testing or is a scope mandatory?



Naw, a scope isn't really mandatory. But it's nice to have for quite a few things.
But the Fluke will be fine for testing resistance and AC/DC voltage, which is fine for reviving a old tube amp or something. Even if you were building a kit, the Fluke would be fine.

A variac (variable AC transformer) is more of a piece to have than a scope. It's nice to be able ramp up a old vintage tube POS and watch the voltage and current levels to chase out suspected shorted caps or wanked tubes.
It's also a nice thing to have to save a power supply transformer or even output transformer damage from a slam of inrush current with shorted cap/caps in the path.
They are also nice to have for testing PS transformers unloaded, testing...etc...

A DC supply is really nice to have for reforming those old multicapacitors and watch current/voltage. Some work will reform, some don't.
I'd love to have a nice 500 volt/200 milliamp DC tube supply with take-offs for 2.5/6.3 volt high current filament windings. Breadboard fun......
Currently, I just have this 600 volt/100 milliamp POS DC supply, it works......

Nonetheless, it's pretty much just good practice to just replace the old coupling caps and electrolytics in a old vintage tube amp. The coupling caps in most budget vintage console stereos were probably nuthin' special with regards to sonics, and probably, or eventually will leak DC into the grid of the next stage.
Electrolytic caps such as the aluminum bodied multisectional cans are still made, but kinda spendy I guess. They have non-aluminum cased multisectional capacitors, (JJ) that are a good price, but requires a clamp to attach to the chassis. (It still looks good if one can attach the clamp to the underside of the chassis.)
The HV Axial style electrolytic capacitors (Sprague,etc) can still be found. And can be used on the underside of the chassis if room is made, to replace some bad sections in a mutisectional cap for example. A guy a can leave the can unhooked, or use the good sections with axial caps.

The tube testers are nice to have to see if a tube is bad or not, which is nice but not really absolutely necessary. As long as you know if the tube is good.
With the variac, you can watch whether the heaters start to glow and if they do, start checking voltages, bias, etc.....in circuit is the best way to find out I guess......
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Postby westend » Tue Jun 27, 2006 1:21 am

All good stuff, Mike. I guess this is in Jim's original theme, "something glowing...". I took the plunge into tubes and bought a Layfayette LA-212 off the Egay. Item :http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=9744059989&rd=1&sspagename=STRK%3AMEWN%3AIT&rd=1. It's no McIntosh but I'll get a feeel for tubes. The seller reports he has rebuilt it. We'll see. Just received a Leak 3400 receiver today, also off the Egay that was "operating perfectly". Except for that little left channel out problem, sheesh. Too bad for that seller as a little work with the iron and cleaning and I'm listening to the Doobie Bros. with a great midrange through this piece of British engineering. This thing is a beast. 270w. peak and I bet it does most of that RMS. . This older SS stuff is amazing. Makes my HT setup sound like a big Ipod. Most of the caps are Elnas w/the bigger ones, Nichicons. It also has discrete left/right and balanced connectors. Big mutha' too, 21 1/2"w. about 40 lbs.. Also got a fairly decent tuner for the tube amp, Pioneer TX- 7500. Man, so much good gear out there.
Pioneer 860, Soundstream 600-4, Directed 1100d, CDT IEK, CDT EF61CF, 2-IDQ-10's NoGOT-No gas on Thurs.




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Mike S.
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Postby Mike S. » Tue Jun 27, 2006 4:30 am

You did good on the little Lafayette push-pull.

A local retired EE audio buddy has some Lafayette output transformers that he pinched out of a integrated amp or a receiver. He's the kind of guy that measures his iron, just to see if it conforms to specs amongst other things.

I'm not sure if those are the same output transformers, but they look the same.
He measured his on the bench, and the OPT's have really excellent bandwidth for what they are.

He was using one of those Lafayette OPT's on a breadboard with tube DC supply, and running a old globe 45 through it. It did sound rather nice.........

I dunno how he managed to use a PP output transformer as a single-ended output transformer........I'll have to ask.

6EU7 is 6.3 volt low noise version of a 12AX7. Same gain of 100, just a 6 volt heater instead of 12 volt. Magnavox used 6EU7 in the old console crap...
Easy to find cheap really, I think Sovtek or somebody still makes them.
Mullard and RCA are about all I've come across.

6CA4/EZ-81 is full wave rectifier. IMHO.......Mullard EZ81 is king. I have a bunch, and a few Mullards.......Mullard EZ81 is spendy.....

You may want to ask the seller what brand of driver and output tubes the amp is using, condition, etc... So whether or not you may need to start searching for tubes.

If it was me, and those OPT's are like what my friend has, I woulda gave the guy 70 bucks just for them....but that's me....

If it works like described, and the guy brags "satisfaction guaranteed", you'll probably have good working amp. He's brave......I just put "AS IS".....

I'll bet that is a nice sounding little vintage 6BQ5 PP........ though I bet I could hear it hum through my Cornwalls.....:cwm10:

I bet that Leak receiver would probably sound pretty interesting on the Klipsch cornwalls. The golden age of the SS power amp era IMO is around '74-'80.
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westend
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Postby westend » Wed Jun 28, 2006 8:07 pm

Thanks for the tube breakdown and the Layfayette info. Looking forward to getting the amp so I can play with some tuners I have. The older SS gear is cheap for the quality it offers. Since the tube gear is getting scarce it seems to be rising in price. I'd need an equity loan to buy a Mcintosh setup off Ebay.
I was thinking of selling the Leak receiver but the thing is so f'n elegant. Really, too nice for the shop and don't know if it fits my plans for the house. I cleaned it and Deoxed all the switches and connectors. It plays awesome through the Aux inputs, as well. Basically, just a two gang FM tuner but the audio section does a great job on local stations. Maybe it's the iron but also might have something to do with the layout and good parts.
I'd even stretch that quality timeline back to about '70. It seems like some of the bigger mfgs. started ramping up their gear to compete right around that time. I've got a Pioneer SX-990 enroute so that should give me a good comparo to ages.
I wish Jim would chime in about the tube gear. Probably too busy listening.
Pioneer 860, Soundstream 600-4, Directed 1100d, CDT IEK, CDT EF61CF, 2-IDQ-10's NoGOT-No gas on Thurs.




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Postby JimJ[VT] » Sat Jul 01, 2006 1:43 pm

What's wrong Jim, a little miffed by the crack habit comment?
You have a pair of 8, 10 watt SET monoblocks with intentions (I think) of building a linestage or pre-amp. You think your just gonna stop after that?

Mod those Forte xovers......trust me.....


Haha...I ended up buying a preamp instead of building one (Rogue Audio 66). Although it didn't have a phono stage like I first thought, so I'll probably end up getting a Bottlehead Seduction (6DJ8's) to handle the phono job.

The speakers stay unmodded for now...dealing with the signal chain in front of them is enough of a project for this summer :) Maybe when I get the rest of the setup purring nicely I'll do something about the speakers. I haven't even taken the grills off in the year and a half that I've owned them :D

I wish Jim would chime in about the tube gear. Probably too busy listening.


The setup's kind of scattered all over the place ATM...waiting on my new pre to arrive. And then find a Technics dealer that can order a '1200MK2 for me. The way I had everything set up was kind of temporary, just to make sure everything was cookin' together :)
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Postby westend » Sat Jul 01, 2006 7:18 pm

Gotcha, Jim. Guitar Center is a registered Technics dealer. I've bought some stuff from them. They aren't the spawn of Satan.
Pioneer 860, Soundstream 600-4, Directed 1100d, CDT IEK, CDT EF61CF, 2-IDQ-10's NoGOT-No gas on Thurs.




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Postby JimJ[VT] » Sat Jul 01, 2006 10:50 pm

I went to a local one...they only stocked the MK5's and MK5G's, and gave me a blank look when I asked if they could special order a MK2...I guess I could try another location around here, there's a couple in the area.
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Postby JimJ[VT] » Sun Jul 02, 2006 10:44 pm

Was just reading this...

And if you come across test gear for cheap, nab it. A good old school volt/ohm meter is a good thing to have, or a vacuum tube volt meter, or a tube tester....etc......you start working on the circuits, you'll have to measure voltages, do some math, test tubes...etc...


While a good tester to measure transconductance is a cool thing to have (and something I probably need to acquire in the future), are VTVM's really needed anymore now that we have DMM's with relatively high input impedances? I've used vacuum-based GDO's before, and I wouldn't wish that on my worst enemies...:)

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