Speaker Recommendation?

PRSplaya:

You were asking about photos; here's some of another GU-12, from an eBay auction:

http://cgi.ebay.com/Vintage-Ampeg-Tube-Amp-GU12-Reverb-Very-Good-shape_W0QQitemZ7379879926QQcategoryZ43372QQrdZ1QQcmdZViewItem

My GU-12 has the original knobs (the usual round black pointer knobs with the brushed insert), and mine has never sat in a flooded basement, as appears to be the case with this one... :(

edit: "Should be putting out somewhere around 20 watts."? Rated plate dissipation on a 7591 is 19 watts; I think he guessed a little low...

C.K.

Cool amp! I've got some bad Ampeg GAS now! Thanks a lot :D

How does this look? V-2
Item number 7379901518 if the link doesn't work. I'll probably be going by there tomorrow, since it's in my drummers town, and I'll be there anyway.

Originally Posted by: PRSplayaHow does this look? V-2
Item number 7379901518 if the link doesn't work. I'll probably be going by there tomorrow, since it's in my drummers town, and I'll be there anyway.

Here's your circuit:

http://www.kbapps.com/audio/schematics/tubeamps/ampeg/v2.html

Your tube complement is 3 x 12AX7, 6CG7, 6K11, 12DW7, 12AU7, and 2 x 7027A, so you might want to head over to a place like tubedepot.com to see what a refresh will run (if needed). 7027As are weird, like 7591s, but they should be just as available now from JJ/Tesla or Sovtek. They don't have the 6K11, but you could probably get one of those NOS from tubesandmore.com (Antique Electronic Supply). I have to do that for my 6U10.

You might have to also convert the 2-conductor AC cord to grounded 3-conductor, and eliminate the "death" capacitor (C21), for safety. I am going to have to do this on my GU-12. There's an electric shock risk there if you're not careful.

I like those sensitivity and high-pass options in the preamp circuits, too.

C.K.

Originally Posted by: PRSplayaHow does this look? V-2
Item number 7379901518 if the link doesn't work. I'll probably be going by there tomorrow, since it's in my drummers town, and I'll be there anyway.

BINGO!!!! :D

That looks to me like a 1977 V-2. Identical amp to the guts of my >salvaged VT-40<. To my ears, the most versatile amp they made. It has Input Sensitivity switches for each channel, and a Master Volume control. Don't be put off by the crap you hear about the Master Volume circuits on other amps. This is an Ampeg. They did it right.

Don't worry about the >6K11< tubes. They are still available for very reasonable cost. And any high-quality >6L6-type< tube will just drop into the power stage.

That's a great job you did on your conversion! I'd love to hear that beast in person! What is that bohemouth on the table that looks like it has a quad of KT-88's?

What do you think would be a reasonable price for that head? Don't want to pay too much for it. Looks to me like it's already got a grounded plug on it. Anything else I should watch out for since I probably won't get to try it out before buying it.

Originally Posted by: LordathestringsAnd any high-quality 6L6-type tube will just drop into the power stage.

Without any socket wiring changes or re-biasing? That would sure make it easy... cool.

C.K.

Originally Posted by: PRSplayaThat's a great job you did on your conversion! I'd love to hear that beast in person![/QUOTE]

Thanks! It's my #1 stage amp. The lil' G-18 is my preferred jam amp, because it sounds great without destroying anyone's hearing.

Originally Posted by: PRSplayaWhat is that bohemouth on the table that looks like it has a quad of KT-88's?[/QUOTE]

That, my friend, is my 1976 VT-22, aka 'The Voice Of Gawd'. A V-4 is the same thing in a separate head instead of a 2x12" combo. And yes, that's a quad of JJ KT88's. :D Just plug 'em in, and set the bias!

Then stand way back!

[QUOTE=PRSplaya]What do you think would be a reasonable price for that head? Don't want to pay too much for it. Looks to me like it's already got a grounded plug on it. Anything else I should watch out for since I probably won't get to try it out before buying it.

Anything you can't actually try out is a bit of a crap-shoot. Prices seem to range from $200 - $400, depending on condition. For $400, it should be in nearly pristine condition, no issues, ready-to-rock.

You should take it to someone who knows about such things to be sure that the 3-prong AC plug was installed correctly. And be very sure that the polarity switch is completely disconnected, along with the AC grounding cap.

Any 30 year old amp is probably due for fresh power supply caps. Take that into account as part of your bidding decisions. If it's been sitting in a closet for a long time, the caps are going to be in rough shape, and at the very least will need to be re-formed. If played often, but not cranked, it should be good to go.

[QUOTE=stahlhart]Without any socket wiring changes or re-biasing? That would sure make it easy... cool.

Follow that 6L6 link in my previous post. My VT-40 (VT-15?) is still running the original Ampeg-labeled 7027A tubes. My VT-22 had two different pairs (?) of 5881's in it. I installed a fresh quad of KT88's. Any time you change the power tubes, you should adjust the bias. Fortunately, it's relatively simple to install a multi-turn trimpot in the bias supply to make the bias adjustable. Much easier than swapping out resistors to try to get the right bias voltage.

Missed that link; sorry...

That's one thing I haven't quite figured out yet on my GU-12. It's got some sort of weird setup for the output -- not your typical adjustable negative DC to the grids.

I'm fairly certain that it has something to do with that "E" feed from the center tap on the filament winding of the power transformer. But there's nothing adjustable from the factory, so I haven't messed with it at all. I did get the Bias-Rite, and I could probably check the cathode current through the two 7591s just to make sure they're reasonably close, and just leave it at that.

I forgot to mention re-capping. I've already done that on mine. Apparently the three capacitors in the tremolo circuit are prone to failing and shutting it down -- when I got mine, the tremolo was dead, but in my case it was the neon lamp / photoresistor module that was bad. So after that I figured I'd go though and completely re-cap it anyway; Orange Drops for the tubulars and new electrolytics.

I guess that if you're really a glutton for punishment, you can measure all of the resistors to see if any have significantly changed value from aging, too... but the GU-12 is working quite well at the moment, so I'm thinking that there isn't anything to far off. At some point I'm going to go through them all, just to make sure, though.

C.K.

This has been a really great discussion, by the way... :)

C.K.

Originally Posted by: stahlhart... I guess that if you're really a glutton for punishment, you can measure all of the resistors to see if any have significantly changed value from aging, too... but the GU-12 is working quite well at the moment, so I'm thinking that there isn't anything to far off. At some point I'm going to go through them all, just to make sure, though. ...

Unless somethings is obviously wrong, there's probably very little to gain from replacing resistors. The originals were +/- 5% tolerance to begin with, and they would have pretty much stopped drifting 20 years ago. In other words, if it ain't broken, don't try to fix it. You could find that you lose the mojo by bringing everything back to exact design values. Or it might sound better. Given the amount of work involved, I'd be inclined to leave it alone unless it was mis-behaving.

Originally Posted by: PRSplayaHow does this look? V-2
Item number 7379901518 if the link doesn't work. I'll probably be going by there tomorrow, since it's in my drummers town, and I'll be there anyway.

Update: Some sniper jumped in grabbed it for $430. I think he overpaid, but it is a very good year of a very good model.

Seeing that auction reminds me... I want to make sleeve-cases for my amps, so I can use them as heads instead of just as combos.

Yeah, they were closed by the time I got there Saturday. I wasn't going to pay anymore than $300 if it was in good enough condition. I also kinda talked myself out of it, since I have enough toys at the moment, and some pretty hefty bills comming up.

In the past 3 years, I believe the best gear purchase I made was buying your Rock Master. I swear there is not a tone I can't get out of it! And to top it off, I just got a bad ass EQ to run it through, so the tone possabilities are limitless. Now all I need is a power amp, and it will become my main rig. Here's my idea :D ... I wan't a 2 channel tube power amp like the Carvin T100 that allows you to run EL34's on one channel and 6L6's on the other channel. I'm gonna split the signal of the rockmaster into the left and right channel of the EQ, then to the power amp, and then into the stereo inputs of my Marshall 4x12. I'm thinking I'm gonna need a forklift to carry that rig it's gonna be so fat. My thinking is, it will give me that layered, dual amp setup tone (I can add a little offset delay in one of the channels with the EQ to give it a little space). Ok, I have to stop now, my head is about to explode :eek:

I used to run my Rock Master into the slave input of my VT-22. I drifted away from that in favour of the simplicity of plugging straight in. hmm... might be worth revisiting...