6au6, 6ar5

[a man called country]

okay, my violinist has just bought himself an amp off ebay running

- 2-6au6
- 1-6ar5

just wondering what sort of wattage this is likely to produce, and, if it's possible (with new sockets) to replace these guys easily with more common tubes?

thanks:)

[erichayes]

A single 6AR5, with 250 volts on the plate, is good for around 3 watts @ 10% THD. You could use a 6AQ5/6005 if you make sure there's nothing connected to pin 7 of the socket. You won't gain anything in output to speak of, but AQ5s are cheaper and easier to find.

The 6AU6, on the other hand, was one of the most ubiquitous tubes ever produced. Look for it as 6AU6, 6AU6A and 6136.

[a man called country]

okay cool:)

and, 6au6 - what sort of wattage are these going to produce?

thanks

[erichayes]

The 6AU6s are small signal pentodes that aren't normally used in audio. In this case, they're being used as preamp and driver tubes. The only tube that's dealing with power is the 6AR5.

[a man called country]

so i guess they're like 12ax7s only mellower?

thanks for all your info!

chris

[erichayes]

Hi Chris,

No, pentodes, in general, are regarded as being inferior to triodes as far as sound quality is concerned. The 6AU6 is a "good" AF pentode, and in the application of your violinist's amp's circuit, I doubt you'd be able to tell the difference between it and a pair of twin triodes. I'm almost positive which amp it is, but if you can post a photo or two, I can nail it down.

[a man called country]

http://cgi.ebay.ca/1960s-LAFAYETTE-TUBE ... dZViewItem

so, a five watt amp - anything i can do to beef 'er up?

[erichayes]

Hi Chris,

I KNEW it. Look at the rim of the speaker and see if there's an ink-stamped model number on it. If there is, let us know. There were some Lafayette amps that used Jensens stock, but a lot of them had the original Japanese speakers replaced with Jensen, CTS, Quam, Utah, or if the owners were really crazy, EV or JBL.

Be satisfied with the 3 or so watts you'll get out of the amp, and leave it untouched. I can't believe you picked it up for the price you paid. The amps of this genre are becoming gold nuggets as studio amps, because they go into distortion so effortlessly. Not my cup of tea, as anyone who's read my threads knows, but a fantastic example of early '60s practice amps--although they didn't call them that back then. The ad copy led you to believe you could play Winterland or Carnegie Hall with your $29.95 Professional Guitar Amplifier.

[EWBrown]

I'll say 6AU6s are ubiquitous... In the Great Plinker Haul of a few years ago, I ended up with over a thousand of 6AU6s and 6AU6As... I gave most of them away to my friend Dave who has an enormous tube "collection", though I still tested and kept about 40 for myself... As I recall I still have a couple dozen 6AR5s buried in the "yet to be triaged and tested" remnants of The Haul.

/ed B in NH

[dragongoff]

I just picked up a Kawai GS-45. It has 2x 6AV6 and 1x 6AR5. I can't find anything on the net about it. Neither Kawai US or Japan knows anything about it either. it's a nice tube sound and find it a different than the usual 12ax7, EL84 type sound. I got it for studio use. A nice guitar sounds amazing through this amp which has only a volume and tone thru a 6" speaker. The speaker says it's an 8 ohm 3 watt so I guess this is a 3 watt amp. Loud enough for studio work.

[TomMcNally]

The lil Kawai has a late 60's early 70's look to it.

You might want to lay the back on a photocopier
and snag the schematic before it wears any more.

Cool !

[dragongoff]

The lil Kawai has a late 60's early 70's look to it.

You might want to lay the back on a photocopier
and snag the schematic before it wears any more.

Cool !

That's an excellent idea. Will do that asap.
Thanks!

According to Kawai US even the older guys at Kawai Japan don't know anything about it. Looks '60's to me with the way the vinyl's patterned. Kawai US thought it might be a rebadged Teisco when Kawai bought Teisco in 1967 or so.. But the only Teisco site on the net, Larry, said it doesn't have any similarities to anything he's seen. Sure is a puzzler...

[erichayes]

That board looks suspiciously similar to one in an amp I restored earlier this year. Some heads-ups:

If they haven't started already, those PIO coupling caps will go leaky. There should be no DC voltage on the grid sides of the caps. If there is, replace them. I replace them whenever I find them, just to minimize the rubber-band effect.

Those funky gray resistors with the values printed on them are notorious for changing value. They can be checked in-circuit to see if they're in the ballpark. Any that aren't should have one lead disconnected and be rechecked.

If you have hum with the volume all the way down, replace the electrolytic caps.

Almost all mid-60s Japanese circuit boards had foil lifting issues, even back then. Now, with 40 years of heat literally baking them, the foil can lift with the slightest amount of mishandling. If you find any problems with the amp, and aren't absolutely comfortable doing the repairs yourself, find an experienced pro to do the work.

[dragongoff]

That board looks suspiciously similar to one in an amp I restored earlier this year. Some heads-ups:

If they haven't started already, those PIO coupling caps will go leaky. There should be no DC voltage on the grid sides of the caps. If there is, replace them. I replace them whenever I find them, just to minimize the rubber-band effect.

Those funky gray resistors with the values printed on them are notorious for changing value. They can be checked in-circuit to see if they're in the ballpark. Any that aren't should have one lead disconnected and be rechecked.

If you have hum with the volume all the way down, replace the electrolytic caps.

Almost all mid-60s Japanese circuit boards had foil lifting issues, even back then. Now, with 40 years of heat literally baking them, the foil can lift with the slightest amount of mishandling. If you find any problems with the amp, and aren't absolutely comfortable doing the repairs yourself, find an experienced pro to do the work.

Thanks so much for the technical advice, specially on an amp of this obscurity. So far there is no noise. I don't see any bubbles or leaks on the caps. Evreything looks clean. It's almost as if it never got much use. It probably sat in someone's closet in Japan. It has Japanese writing on one side in magic marker. Have no idea what it means..Something the original owner put on there.

What type/brand caps/ resistors would you recommend in case they need changing?

What is the rubber band effect?

And what was the amp you restored that looked like this board? I'm trying to find out history on this...

[erichayes]

The guy who has the amp is out on tour and his wife can't find it, so I'll just have to wait until he checks in. Almost all of those amps were built by Original Equipment Manufacturers (OEMs) like Matsushita, Hitachi, Toshiba, Trio etc for second-steppers like Lafayette, Western Auto, Radio Shack etc, who would put their brand names on them and sell them "exclusively". Usually, the only differences between amps of the same OEM were the speaker size and whether or not it had tremolo.

When I spoke of leaky coupling caps, I was referring to electrical leakage, although those particular caps did leak physically as well. If, indeed, the amp led a benign life, there might not be that much heat damage and the caps could be good to go for a while. The resistors, on the other hand, are losers out of the chute. I had some NOS I picked up at a hamfest that were all over the map--high, low, and one or two that were dead on.

For replacement caps, I'd use either SBE Orange Drops or Illinois metallized polyprops. Xicons are OK if you're on a budget, but I don't know what long term heat effects there might be.

For resistors, I use Xicon small size metal oxide or NTE 2% flameproof (also metal oxide). MO can handle the heat much better than carbon film or composition resistors do, and they don't drift with age. A small size 1 W MO is virtually the same physical size as a ½ W composition, so there isn't a space issue.

The rubber band effect is the result of an incompetent, lazy or inexperienced tech doing a half-assed repair on a piece of equipment, causing it to snap back into the shop until the job is finally done properly.