Rocket 2

Small combos like Mercury and Jet, Jess Oliver's fliptop Portaflex, the Gemini, Echotwin, B25, V4, VT22 up to the 300 watt SVT

Re: Rocket 2

Postby RWood on Sat Aug 21, 2010 5:13 pm

PeterS wrote:RWood wins the Long-Distance Diagnosis prize for this week.


Yay!

Don'tcha love it when you can do a repair that doesn't even require parts?

Does your amp's back panel have a schematic? I have a copy but could use an upgrade. Btw, the only difference between the circuit on that Rocket 2 and my Gemini IV is that yours has two input jacks.......mine four. Electronically they are twins.

Glad your amp is working,

RWood
RWood
Page
 
Posts: 307
Joined: Thu Mar 16, 2006 7:49 pm
Location: Richmond, VA

Re: Rocket 2

Postby PeterS on Sat Aug 21, 2010 5:59 pm

The back panel has the schemo in somewhat rough shape. There's the same schemo in this thread that I found, scroll down, there's a fairly clear version near the end:

http://www.thegearpage.net/board/showth ... p?t=553796

I haven't checked the entire amp vs. the schemo but I found a coupla minor differences in resistor values already.

Gemini IV is quite rare, isn't it? As is Rocket II. Funny to have 2 near-identical models... and what happened to Geminis 3 and 5?
PeterS
King
 
Posts: 6156
Joined: Tue Sep 13, 2005 4:07 pm
Location: Canada

Re: Rocket 2

Postby RWood on Sat Aug 21, 2010 7:35 pm

Thanks, those two pictures at the end are better than what I had.

Yes, Gemini IV is rare. I talked to Gregg about it when he was putting the book together, and it was the first he'd heard of a model IV. His publisher paid to have the amp shipped to St Louis, and it wound up pictured and mentioned in The Story Behind the Sound. It was made in mid 1964.

It was very interesting to find that the amp has a first cousin, though, and I agree with you that there aren't lot of Rocket 2s around, much less ones with the 7199 driver/splitter. Nice amps; I like how they sound when fully cranked, in a decent sized room. I used to gig with the Gemini and a Gretsch and it was really one of the few time periods when I was satisfied with my tone.

RWood
RWood
Page
 
Posts: 307
Joined: Thu Mar 16, 2006 7:49 pm
Location: Richmond, VA

Re: Rocket 2

Postby PeterS on Wed Feb 23, 2011 2:11 am

Bah, I can repair pretty much any amp that has the decency to be properly broken, but I'm suffering the cursed :evil: intermittent fault :evil: .

A while after I thought I had the Rocket II all sorted out, it developed an intermittent hum. I resoldered every pin on every tube socket, and most of the eyelet board (including every ground connection).

Do filter caps ever go intermittent? Could be a short somewhere that draws current and pulls the power supply down, that would make a hum...
PeterS
King
 
Posts: 6156
Joined: Tue Sep 13, 2005 4:07 pm
Location: Canada

Re: Rocket 2

Postby Baron Von Machinenmann on Wed Feb 23, 2011 1:10 pm

Have you scoped the hum or is it the "normal" 120 hz variety?
ImageImageImage

John Lennon/Jimi Hendrix/Jimmy Page Fan
Baron Von Machinenmann
Administrator of Mirth
 
Posts: 17323
Joined: Sat Mar 08, 2003 8:01 am
Location: Central, New York

Re: Rocket 2

Postby PeterS on Wed Feb 23, 2011 2:41 pm

Haven't scoped it but it sounds like 120. Are you thinking motorboating? Certainly possible,old amp with original caps. Maybe I should just recap it anyway...
PeterS
King
 
Posts: 6156
Joined: Tue Sep 13, 2005 4:07 pm
Location: Canada

Re: Rocket 2

Postby Baron Von Machinenmann on Wed Feb 23, 2011 5:16 pm

I've temporarily jumpered in caps across the originals terminals in circuit just to see if there is an improvement before I go through the hassles of totally removing a can type. :wink:
ImageImageImage

John Lennon/Jimi Hendrix/Jimmy Page Fan
Baron Von Machinenmann
Administrator of Mirth
 
Posts: 17323
Joined: Sat Mar 08, 2003 8:01 am
Location: Central, New York

Re: Rocket 2

Postby PeterS on Wed Feb 23, 2011 7:11 pm

That's a good technique.

The caps seem good, in that there's no hum some of the time, and there's plenty of thump. But that could mean the first cap is good... if the later ones for the preamp are bad that could make motorboating...
PeterS
King
 
Posts: 6156
Joined: Tue Sep 13, 2005 4:07 pm
Location: Canada

Re: Rocket 2

Postby Gooch on Wed Feb 23, 2011 10:33 pm

Back to your original post, I think he'd be very lucky to see $400 for that amp. I sold one in 2008 for $200. That's all I could get out of it.
Dying ain't much of a living.
Gooch
Baron
 
Posts: 2513
Joined: Sat Jun 16, 2001 7:01 am
Location: Austin TX

Re: Rocket 2

Postby PeterS on Thu Feb 24, 2011 2:13 am

I think Ampegs might go a bit higher round here due to rarity.

Now I know when you have an intermittent fault you should never say "I think I fixed it", because that just means it has gone into hiding for a while (and is laughing at you). However, I think I fixed it. Finally got it making the hum while I had the chassis out. Started measuring the voltage at each power supply node, and when I put the probe on one of them the hum stopped. Tapped at it, hum came and went. Resoldered the joint, no hum, AND THE RADIO PICKUP IS GONE TOO. Weird that a bad joint in the power supply (not say, a grid circuit) can have that effect.
PeterS
King
 
Posts: 6156
Joined: Tue Sep 13, 2005 4:07 pm
Location: Canada

Re: Rocket 2

Postby RWood on Thu Feb 24, 2011 8:38 pm

Glad you found it (again). Was this the same pin you had trouble with last time? I wonder of the socket itself is losing tension.
RWood
Page
 
Posts: 307
Joined: Thu Mar 16, 2006 7:49 pm
Location: Richmond, VA

Re: Rocket 2

Postby PeterS on Thu Feb 24, 2011 8:53 pm

No, different spot, this time on the eyelet board, first time was a tube socket. Call me an idiot for resoldering HALF the eyelet board the first time. SO now I should go back and do the rest... maybe tomorrow.

THe power tube sockets aren't great, despite my retensioning. Any special retensioning tricks short of replacing them?
PeterS
King
 
Posts: 6156
Joined: Tue Sep 13, 2005 4:07 pm
Location: Canada

Re: Rocket 2

Postby Baron Von Machinenmann on Thu Feb 24, 2011 9:24 pm

I use a straight dental pick and coerce each side inwards slightly beyond center as there will be a degree of spring back. :thumbsup:
ImageImageImage

John Lennon/Jimi Hendrix/Jimmy Page Fan
Baron Von Machinenmann
Administrator of Mirth
 
Posts: 17323
Joined: Sat Mar 08, 2003 8:01 am
Location: Central, New York

Re: Rocket 2

Postby PeterS on Thu Feb 24, 2011 11:52 pm

That's about what I've been doing, maybe I need to go a bit more extreme.
PeterS
King
 
Posts: 6156
Joined: Tue Sep 13, 2005 4:07 pm
Location: Canada

Re: Rocket 2

Postby PeterS on Sat Jan 14, 2012 10:32 pm

Well, back at this thing... tube socket problem turned out to be undersize pins on JJ power tubes (7591). Grrr. Works fine with some worn out old Westinghouses.

Intermittent hum came back and this time I tracked it down with the scope, it was the pentode section of the 7199 tube. Yes I had tried swapping tubes but I had swapped in another noisy one! I only have one 7199, but I have a socket adaptor and about three each of 6BL8 and 6U8. The 6U8's all hum, the 6BL8's are much better. The gain is a little lower but it hardly matters --- the triode is used as a split load phase inverter, so the gain is irrelevant. The pentode is inside the feedback loop of the amp, so changes in gain are reduced by the feedback. It seems like these pentodes* are somewhat prone to hum from the heater-to-cathode leakage. Probably wouldn't matter if the cathode resistor was bypassed, but in this amp it isn't, because the cathode is used for the feedback connection.

* reading around, it sounds like 6u8 etc were mostly for RF use, not audio, so hum is probably not an important spec.
PeterS
King
 
Posts: 6156
Joined: Tue Sep 13, 2005 4:07 pm
Location: Canada

PreviousNext

Return to Ampeg

Who is online

Users browsing this forum: No registered users and 1 guest