NAD - Reverb dumpster dive

fitz said:
$175.
But it came without the reverb tank and I "negotiated" a $25 refund to cover most of the cost of the one I got from Tubes & More.
Tube cage was another $27 and I got about $25 more in corners/handle/feet stuff from T&M.
Tolex / grill for the head and pending pair of 1x12 cabs will run about another $100.
Click to expand...
That was a good deal for $175 :shock: .
Fredericksburg?
Leesburg?
Pittsburgh?
 
fitz said:
Thanks.
The PCB boards in it are all stamped JTM60.
I'm going to keep it inverted in the headshell like the pics above - keep the tubes on top.

Closest thing I have to compare it to is my DSL20, although it has a smoother clean channel that breaks up to a more classic tone with volume, and the overdrive channel is a lot like my 5010 cranked, but with a definite tube feel and way more volume on tap.
Keep in mind, I still have to replace the presence pot, and I have no idea what the snapped of shaft is set at.

I tried running through another 212 cab with V30's today, but I think I like the V-Types better with this amp.
I also have a pair of T-75's in the closet that I will give a try when I get the new cabs made.
I'd love to run it through some greenbacks, or H-30 anniversaries I have, but I might like it too much and worry about the power handling when it's cranked.
Click to expand...
Been a long time since seeing the JCM 600 ( probably 25 years now? Lol) But i did go grab an old product catalog they issued when it and the JCM2000 came out. Looks like the cab they used to pair the head was a Marshall C410A with 30w Celestion Gold Backs, 120w 16ohm.

The combo versions of this amp ( 601 and 602) used a single Celestion G12-65 Heritage 65w in the 601 and two Celestion G12-65 Heritage 65w in the 602

Hope this helps!
 
Clockworkmike said:
Been a long time since seeing the JCM 600 ( probably 25 years now? Lol) But i did go grab an old product catalog they issued when it and the JCM2000 came out. Looks like the cab they used to pair the head was a Marshall C410A with 30w Celestion Gold Backs, 120w 16ohm.

The combo versions of this amp ( 601 and 602) used a single Celestion G12-65 Heritage 65w in the 601 and two Celestion G12-65 Heritage 65w in the 602

Hope this helps!
Click to expand...
This chassis was originally a 601.
The speaker jacks are labeled Internal & Extension, and the 602 was a wider chassis for the 2x12.
The head was labeled with the impedance for the whacky switch jacks.
One 16 and one 8, but will switch both jacks to run parallel 16's on the 8 ohm tap.

I've never tried a G12-65.
Celestion says they're like a high power greenback, but I've heard similar things about the creambacks.
Might be another rabbit hole I'm destined to be sucked into...

edit: I forgot to mention, I have a 1965A w/ G10M-30's and a 1695B with original G10L-35's.
I also have those little 2x10 columns with an M30 & V-T jr. in each I could try for that 4x10 vibe.
 
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fitz said:
Thanks.
The PCB boards in it are all stamped JTM60.
I'm going to keep it inverted in the headshell like the pics above - keep the tubes on top.

Closest thing I have to compare it to is my DSL20, although it has a smoother clean channel that breaks up to a more classic tone with volume, and the overdrive channel is a lot like my 5010 cranked, but with a definite tube feel and way more volume on tap.
Keep in mind, I still have to replace the presence pot, and I have no idea what the snapped of shaft is set at.

I tried running through another 212 cab with V30's today, but I think I like the V-Types better with this amp.
I also have a pair of T-75's in the closet that I will give a try when I get the new cabs made.
I'd love to run it through some greenbacks, or H-30 anniversaries I have, but I might like it too much and worry about the power handling when it's cranked.
Click to expand...
Replacing board mounted pots is tricky. Do you have a solder sucker? Be very gentle with the solder iron. The pcb is fragile.
I replaced pots on the JTM30 I had briefly.
www.adafruit.com

Engineer Professional Silicone-Tip Solder Sucker

Ever go to a diner and they give you a bottle of ketchup and it says "Extra Fancy" and you're thinking to yourself "what makes this ketchup 'extra fancy' ...
www.adafruit.com www.adafruit.com
 
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Yes, I have a cheapie solder sucker that came with my iron.
Works well enough.
I just replaced all 6 pots, the 3 front panel jacks, and the output transistors in my 5010.
I'm actually contemplating running wires from the PCB and putting the presence pot in the front panel where the parallel loop mix knob is.
And vice versa moving the mix knob to the back panel by the speaker jacks.
 
Clockworkmike said:
Been a long time since seeing the JCM 600 ( probably 25 years now? Lol) But i did go grab an old product catalog they issued when it and the JCM2000 came out. Looks like the cab they used to pair the head was a Marshall C410A with 30w Celestion Gold Backs, 120w 16ohm.

The combo versions of this amp ( 601 and 602) used a single Celestion G12-65 Heritage 65w in the 601 and two Celestion G12-65 Heritage 65w in the 602

Hope this helps!
Click to expand...
I hate to bring this up but
it looks like the power amp circuit board might be the same as JCM 2000 :eek: also the same as a marshall "orange crush."
:eek::eek: it might have the bias drift issue better check that.
 
ibmorjamn said:
Replacing board mounted pots is tricky. Do you have a solder sucker? Be very gentle with the solder iron. The pcb is fragile.
I replaced pots on the JTM30 I had briefly.
www.adafruit.com

Engineer Professional Silicone-Tip Solder Sucker

Ever go to a diner and they give you a bottle of ketchup and it says "Extra Fancy" and you're thinking to yourself "what makes this ketchup 'extra fancy' ...
www.adafruit.com www.adafruit.com
Click to expand...
You can use solder wick (make sure the copper is clean and bright). Oxidized copper will not work.
1674570989221.jpeg
and soak the wick in rosin flux before you un-solder.
615224.jpg
Using that method your solder removal will be much much faster.

2. Clean the flux off the cooled circuit board with 91% isopropyl alcohol and a toothbrush.

images
 
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Got the tube shield / cage from Reverb today, along with the new reverb tank & presence pot from Tubes & More.
Reverb is working fine on both channels from the individual controls.
I was able to drill & tap a small machine screw into the broken pot shaft yesterday (I can adjust it with a screwdriver now).
So I know everything is working on the circuit side and I just need to swap out that pot.
PXL_20230126_001339587.jpg
I'm taking Friday off work for my Birthday and plan to get started on the cab builds.

So far, the amp purchase and parts are at $180, and it looks like the cab build supplies will run around $250.
The X going to get me a T&M gift certificate and feed me lasagna for my birthday (still good friends), so my build costs may be looking even better...
 
fitz said:
Got the tube shield / cage from Reverb today, along with the new reverb tank & presence pot from Tubes & More.
Reverb is working fine on both channels from the individual controls.
I was able to drill & tap a small machine screw into the broken pot shaft yesterday (I can adjust it with a screwdriver now).
So I know everything is working on the circuit side and I just need to swap out that pot.
View attachment 88614
I'm taking Friday off work for my Birthday and plan to get started on the cab builds.

So far, the amp purchase and parts are at $180, and it looks like the cab build supplies will run around $250.
The X going to get me a T&M gift certificate and feed me lasagna for my birthday (still good friends), so my build costs may be looking even better...
Click to expand...
Happy Birthday, good work.
 
Swapped out the broken shaft presence pot last night.
Also made a cover for the stupid vent holes under the power tubes.
There is a ground screw through the chassis just behind the mains plug, so I cut a piece of aluminum to size and drilled a hole at the ground screw.

PXL_20230127_041852063.jpg

Just one bias trim pot, and the TAD tubes that came with the amp were far from balanced.
Swapped out the power tubes with a matched pair of "vintage" CVC clear glass tubes I have.
Not as bright as the TAD's, but they work well with the tone of this amp, and the now functional presence pot can get a nice range of mellow to bright.

PXL_20230127_041936440.jpg

Going to start the cab builds today - I think I'll do a separate thread for pics on that.
 
fitz said:
Swapped out the broken shaft presence pot last night.
Also made a cover for the stupid vent holes under the power tubes.
There is a ground screw through the chassis just behind the mains plug, so I cut a piece of aluminum to size and drilled a hole at the ground screw.

View attachment 88654

Just one bias trim pot, and the TAD tubes that came with the amp were far from balanced.
Swapped out the power tubes with a matched pair of "vintage" CVC clear glass tubes I have.
Not as bright as the TAD's, but they work well with the tone of this amp, and the now functional presence pot can get a nice range of mellow to bright.

View attachment 88655

Going to start the cab builds today - I think I'll do a separate thread for pics on that.
Click to expand...
Are you going to make some eevil modifications?
doctor-evil-plan-diabolique.gif

I think the vent holes are supposed to allow heat to dissipate and escape from inside the chassis and rise up (?) Heat would rise.....
Maybe with the holes closed the chassis will become too hot inside where to power tubes are located??
 
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fitz said:
This chassis was originally a 601.
The speaker jacks are labeled Internal & Extension, and the 602 was a wider chassis for the 2x12.
The head was labeled with the impedance for the whacky switch jacks.
One 16 and one 8, but will switch both jacks to run parallel 16's on the 8 ohm tap.

I've never tried a G12-65.
Celestion says they're like a high power greenback, but I've heard similar things about the creambacks.
Might be another rabbit hole I'm destined to be sucked into...

edit: I forgot to mention, I have a 1965A w/ G10M-30's and a 1695B with original G10L-35's.
I also have those little 2x10 columns with an M30 & V-T jr. in each I could try for that 4x10 vibe.
Click to expand...
Do you know how to do a bias stability test?
If this amp is using the black plastic bias adjust pot, you might want to replace it with a new one.
pottr22k_small.jpg


The reason is that the bias depends on the wiper of the pot.
When the wiper of the pot fails, the bias shuts off. Then the power tubes red plate.
The wiper can fail on these pots therefore recommend using a fresh pot every 50,000 miles.

Further
it is desirable to change the bias adjustment so that the bias is protected against wiper failure.
This change is rather a simple modification.
Earlier amps such as Plexi were designed to protect against wiper failure, but later amps such as jcm 2000 were not protected.
 
Amp Mad Scientist said:
Are you going to make some eevil modifications?
View attachment 88657

I think the vent holes are supposed to allow heat to dissipate and escape from inside the chassis and rise up (?) Heat would rise.....
Maybe with the holes closed the chassis will become too hot inside where to power tubes are located??
Click to expand...
Those amps were all combo style tubes on the bottom configuration - even the head.
The vent holes let the tube heat rise up through the chassis and cook the boards.
I'm leaving mine inverted, so yeah, all the knob labels on the faceplate are upside down.
I put peel 'n stick letters on the knobs - I can't read those microscopic labels anyways...
Pro tip: Turn knob right for more, turn knob left for less. (y)
PXL_20230124_023958907.jpg
 
Amp Mad Scientist said:
Do you know how to do a bias stability test?
If this amp is using the black plastic bias adjust pot, you might want to replace it with a new one.
pottr22k_small.jpg


The reason is that the bias depends on the wiper of the pot.
When the wiper of the pot fails, the bias shuts off. Then the power tubes red plate.
The wiper can fail on these pots therefore recommend using a fresh pot every 50,000 miles.

Further
it is desirable to change the bias adjustment so that the bias is protected against wiper failure.
This change is rather a simple modification.
Earlier amps such as Plexi were designed to protect against wiper failure, but later amps such as jcm 2000 were not protected.
Click to expand...
One bias pot (not that black one) for up/down on both (AFAIK).
There's not side to side, or individual pots to balance the 2 tubes.
I'll get a pic next time the chassis isn't bolted in the head shell.
 
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