6g15 reissue rebuild questions!

jbennett

Joined: Mar 29, 2011
Posts: 110
Brooklyn, New York

Posted on Mar 21 2012 09:49 PM

A Surf Fragment...

That's a recording I made tonight. Wanted to make a sample of my re-built reverb unit in semi high-fidelity.

Dwell-4
Mix-7
Tone-5

Tremolux on 3.5 in the normal channel.

It was a good excuse to dust off the microphone and mic-pre. Big improvement over the built in imac mic of course.

Last edited: Mar 21, 2012 21:51:26

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tubeswell

Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
Antarctica

Posted on Mar 22 2012 12:15 AM

Sounds like a million bucks!

—

He who dies with the most tubes... wins

Surf Daddies

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jbennett

Joined: Mar 29, 2011
Posts: 110
Brooklyn, New York

Posted on Mar 22 2012 08:12 AM

Thanks T.

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vintagesurfdude

Joined: Nov 28, 2011
Posts: 795
Prescott Valley, AZ
United States

Posted on Mar 22 2012 01:24 PM

Sweet!

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jbennett

Joined: Mar 29, 2011
Posts: 110
Brooklyn, New York

Posted on Mar 26 2012 02:37 PM

Okay. I've found one error I made in my circuit. Maybe someone can tell me if it could possibly be the culprit for my Dwell issues.

Under the doghouse, between two of the electrolytic caps I placed a 1K-2W resistor. The schematic calls for a 10K-1W resistor. Other than some rounded up/down capacitors on the main board this is the only discrepancy that I've found in my circuit and it's off by ten fold.

I thought this was just a bleeder resistor though so I don't see how this would make a difference, and I have looked at tons of photos of vintage units that used several values in that spot under the doghouse.

(yes, that's a Brown/Black/Red/Silver resistor, 1K, not a 10K which would be Orange instead of Red.)

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tubeswell

Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
Antarctica

Posted on Mar 27 2012 12:40 AM

No - changing the supply resistor there won't affect the functioning of the dwell pot. That supply resistor determines the B+ rail voltages in the pre-amp, so a lower resistance will just mean that the B+ voltage is higher for the pre-amp tubes (which would manifest itself in more clean headroom in the pre-amp all other things being equal).

Another thought that occurs to me is that the .01uF coupling cap going from the V1a plate to the dwell pot input lug could be leaking a little DC (although DC would usually make a pot scratchy for all of its rotation). You can check the cap by unsoldering the connection from the cap to the pot input lug, and then hooking up your VDC meter to that (unconnected) cap end and turning the amp on to see if there's a DC reading on your meter. There shouldn't be any DC there. (You will need to start with the meter on the highest VDC measurement setting and then progressively turn it down to the lowest - in case there is a lot of DC on the pot - which BTW I wouldn't expect). If there is any DC on that cap, replace the cap.

—

He who dies with the most tubes... wins

Surf Daddies

Last edited: Mar 27, 2012 00:44:06

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jbennett

Joined: Mar 29, 2011
Posts: 110
Brooklyn, New York

Posted on Apr 01 2012 01:53 PM

So... I took out the chassis again, swapped in a 1w-10K resistor between the electrolytics.

Dropped in a 12AT7 tube and powered it up.

The buzz was GONE, and then it swelled up again, and then disappeared... so now it was intermittent. I noticed that as I put pressure on the dwell knob the buzz would fade out or fade in.

So, I loosened up the dwell pot and wrapped some buss wire under the pot and wrenched it back down figuring it might have been poor contact with the pot. I think this something Tubeswell suggested. That it could be the grounding of the dwell pot. Sure enough that did it.

I think the reason I ruled that out earlier was I jumped (with a 2 foot cable the pot to the chassis and still had the buzz and maybe it was interference that I was getting on that long jumper? I don't know.

Anyway, now I've got a 12AT7 in there, the correct resistor so now the circuit is just like a vintage unit, with the exception of the PT and full wave rectifier.

It sounds great (I like it better with the 12AT7) and thanks again to everyone, especially Tubeswell, for chiming in. I'm glad to have the last of the bugs worked out.

JB

Here are those improved solder joints on the brass...
60w iron to the rescue.

The final guts:

and the new 1w-10K resistor under the doghouse:

Last edited: Apr 01, 2012 14:03:59

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dubtrub

Joined: Sep 22, 2007
Posts: 245
Bakersfield CA.
1 Link Pin

Posted on Apr 01 2012 11:20 PM

Thanks for a great topic. It was very interesting and educational following throughout the entire project.

—

Danny Ellison aka dubtrub

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Bob_Kennedy

Joined: Feb 27, 2012
Posts: 316
Mesa, AZ.
United States

Posted on Apr 02 2012 01:54 AM

JB, you do some clean work & great photography! I've enjoyed this thread thoroughly. Glad you got rid of that dwell pot gremlin. Now crank that reverb!

—

Otto & The Ottomans
Kennedy Custom Guitars

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tubeswell

Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
Antarctica

Posted on Apr 02 2012 02:43 AM

Yep well done JB! Really satisfying when you get your own build sorted - a real achievement.

—

He who dies with the most tubes... wins

Surf Daddies

Top

jbennett Joined: Mar 29, 2011 Posts: 110 Brooklyn, New York	Posted on Mar 21 2012 09:49 PM A Surf Fragment... That's a recording I made tonight. Wanted to make a sample of my re-built reverb unit in semi high-fidelity. Dwell-4 Mix-7 Tone-5 Tremolux on 3.5 in the normal channel. It was a good excuse to dust off the microphone and mic-pre. Big improvement over the built in imac mic of course. Last edited: Mar 21, 2012 21:51:26 Top
tubeswell Joined: Sep 24, 2011 Posts: 1424 Wellington, NZ	Posted on Mar 22 2012 12:15 AM Sounds like a million bucks! — He who dies with the most tubes... wins Surf Daddies Top
jbennett Joined: Mar 29, 2011 Posts: 110 Brooklyn, New York	Posted on Mar 22 2012 08:12 AM Thanks T. Top
vintagesurfdude Joined: Nov 28, 2011 Posts: 795 Prescott Valley, AZ	Posted on Mar 22 2012 01:24 PM Sweet! Top
jbennett Joined: Mar 29, 2011 Posts: 110 Brooklyn, New York	Posted on Mar 26 2012 02:37 PM Okay. I've found one error I made in my circuit. Maybe someone can tell me if it could possibly be the culprit for my Dwell issues. Under the doghouse, between two of the electrolytic caps I placed a 1K-2W resistor. The schematic calls for a 10K-1W resistor. Other than some rounded up/down capacitors on the main board this is the only discrepancy that I've found in my circuit and it's off by ten fold. I thought this was just a bleeder resistor though so I don't see how this would make a difference, and I have looked at tons of photos of vintage units that used several values in that spot under the doghouse. (yes, that's a Brown/Black/Red/Silver resistor, 1K, not a 10K which would be Orange instead of Red.) Top
tubeswell Joined: Sep 24, 2011 Posts: 1424 Wellington, NZ	Posted on Mar 27 2012 12:40 AM No - changing the supply resistor there won't affect the functioning of the dwell pot. That supply resistor determines the B+ rail voltages in the pre-amp, so a lower resistance will just mean that the B+ voltage is higher for the pre-amp tubes (which would manifest itself in more clean headroom in the pre-amp all other things being equal). Another thought that occurs to me is that the .01uF coupling cap going from the V1a plate to the dwell pot input lug could be leaking a little DC (although DC would usually make a pot scratchy for all of its rotation). You can check the cap by unsoldering the connection from the cap to the pot input lug, and then hooking up your VDC meter to that (unconnected) cap end and turning the amp on to see if there's a DC reading on your meter. There shouldn't be any DC there. (You will need to start with the meter on the highest VDC measurement setting and then progressively turn it down to the lowest - in case there is a lot of DC on the pot - which BTW I wouldn't expect). If there is any DC on that cap, replace the cap. — He who dies with the most tubes... wins Surf Daddies Last edited: Mar 27, 2012 00:44:06 Top
jbennett Joined: Mar 29, 2011 Posts: 110 Brooklyn, New York	Posted on Apr 01 2012 01:53 PM So... I took out the chassis again, swapped in a 1w-10K resistor between the electrolytics. Dropped in a 12AT7 tube and powered it up. The buzz was GONE, and then it swelled up again, and then disappeared... so now it was intermittent. I noticed that as I put pressure on the dwell knob the buzz would fade out or fade in. So, I loosened up the dwell pot and wrapped some buss wire under the pot and wrenched it back down figuring it might have been poor contact with the pot. I think this something Tubeswell suggested. That it could be the grounding of the dwell pot. Sure enough that did it. I think the reason I ruled that out earlier was I jumped (with a 2 foot cable the pot to the chassis and still had the buzz and maybe it was interference that I was getting on that long jumper? I don't know. Anyway, now I've got a 12AT7 in there, the correct resistor so now the circuit is just like a vintage unit, with the exception of the PT and full wave rectifier. It sounds great (I like it better with the 12AT7) and thanks again to everyone, especially Tubeswell, for chiming in. I'm glad to have the last of the bugs worked out. JB Here are those improved solder joints on the brass... 60w iron to the rescue. The final guts: and the new 1w-10K resistor under the doghouse: Last edited: Apr 01, 2012 14:03:59 Top
dubtrub Joined: Sep 22, 2007 Posts: 245 Bakersfield CA.	Posted on Apr 01 2012 11:20 PM Thanks for a great topic. It was very interesting and educational following throughout the entire project. — Danny Ellison aka dubtrub Top
Bob_Kennedy Joined: Feb 27, 2012 Posts: 316 Mesa, AZ.	Posted on Apr 02 2012 01:54 AM JB, you do some clean work & great photography! I've enjoyed this thread thoroughly. Glad you got rid of that dwell pot gremlin. Now crank that reverb! — Otto & The Ottomans Kennedy Custom Guitars Top
tubeswell Joined: Sep 24, 2011 Posts: 1424 Wellington, NZ	Posted on Apr 02 2012 02:43 AM Yep well done JB! Really satisfying when you get your own build sorted - a real achievement. — He who dies with the most tubes... wins Surf Daddies Top

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6g15 reissue rebuild questions!