I did that for another head.  Its OK, but you can round the edges and corners better with 3/4 inch stock.   Have you considered 3/4 pine ?

I made one head cab of pine and it worked out fine.  I only used the thin ply because I wanted to use up some stuff I had lying around.   I wouldn't do it again, though.

I have tried different slope values on my OTS 50.
The original was 150K.
I was looking for a spongier, more compressed sound.

Had 68K in there for a whlie.
At first I really liked the change but after a while I wasn't so sure.
It was more spongy and compressed but was also a bit dull and made the tone controls much less responsive.
Currently using 100K which seems to be a good compromise for now.

Changing the slope resistor makes quite a big difference in the feel and response, so worth playing with.

The Xotic EP Booster comes highly recommended too, but I've never tried one.

As I understand it, the PAB simply bypasses the tone stack, which results in more signal getting through.  So its not really a true boost, you're just removing attenuation caused by the tone stack.
The difference in volume is less apparent in the OD channel than the clean channel because the OD signal is compressed.

The solution for you might be a clean boost pedal.  You could use it to boost the signal when engaged, or you can use it as an 'underdrive' - setting its gain low so when you disengage it, you get a 'boost'.   I don't use pedals anymore but I used to have an Xotic RC Booster and would give it a high recommendation.

I wonder if something was wonky from day 1.   After replacing the 1 ohm resistor and putting back the pair of JJ's I've been using for the last year, the bias measurement was a lot closer from tube to tube.

Anyway, I did the slope resistor mod - with a temporary internal switch from 100K to 68K.  Been playing with the 68K and loving it!  Still have to see how it sounds at gig level, but sounding rather stellar at home.
I'm also running the bias a bit cooler than before.  Found a bias calculator online - and now that I know the voltage on the pins, I can bias more accurately.  Apparently, the higher the voltage, the lower the bias setting to get the same dissipation.

The amp is starting to sound like what I bought it for.   Can't wait to gig with it this weekend.

Thanks again to  plasticvonaband, Pickmaster and others who've been so generous with their knowledge and skill.

Hopefully, it won't happen again.  Its unusual for a resistor to just quit with no sign of burn, isn't it ?

Anyway, another question - really for Pickmaster, but since we're already talking and you may know the answer....

While at the electronics store I bought some extra 100K and 68K resistors to try Pickmaster's slope resistor mod.
I couldn't find any brown ones like the one that's in there, so I just got plain carbon fibre, 2 Watters.
I believe the slope resistor is 3W.  I don't know if the brown ones are carbon fibre or what.

Can I put that 2 Watt resistor in there ?

Bypassed the 1 ohm resistor and all is well.  Going to get a replacement now.
Thanks Gregg.  You saved me a small bundle.
Cheers,
Jon

Muchos Gracias, Gregg. I'll give that a try.

What I need to know, if you can tell me, is if I can safely bypass that 1 ohm resistor just to see if that 'fixes' the problem.
If so, I can replace the resistor myself.
If its not safe to bypass, or if the bypass doesn't fix the problem, then I'll probably have to take it to a tech, which I can't really afford right now.

I'm getting 469 V on pin 3. Master Volume is turned off.

Unplugging the C-lator with the amp on is ok if the volume is low. Its never been a problem - I don't think connecting/disconnecting it can harm the amp.  Maybe blow a speaker if the volume is up.

THanks Gregg,
I (sort of) understand what the 1 ohm resistor is for - converting mA to mV so you can easily measure the bias.
What I'm wondering is if I can bypass that resistor with a piece of straight wire to see if that gets V5 working again.
I know I can't measure that side in that case.

I want to see if the problem is just the resistor, or there's something else going on upstream from there.

Pins 8 & 1 are connected together and are getting voltage - the same reading as at the bias lug.  around 35 mV.
And it changes as I adjust the bias pot. I don't understand how that's possible if the resistor is not passing any current.

Or is it just that pins 1 & 8 are not grounded ? Could that be why V5 is not firing up ?

Did some more research and now I'm sure the problem is with V5.
With any tube in V5 and no tube in V4, I get no sound.

Seeing as how the bias current gets to the tube through that 1 ohm resistor and its open, the current's not getting there, even though I get a reading.

So, I'm wondering - can I bypass that 1 ohm resistor and see if that fixes the problem ?
V5 should then get sound even if V4 is pulled out ?

What I don't understand is - if that resistor is creating an open circuit, where are the mV on pins 1 & 8 coming from ?
Why don't pins 1 & 8 read zero mV ?

More info -
The bias resistors (1 ohm)

The one for V4 reads about 1.3 ohms.

The one for V5 seems dead - infinite ohms - no signal getting through
No visible sign of damage or burn on it.

This would indicate to me the problem is V5, not V4.
Tubes are supposed to get fairly hot,  no ? 
For a power tube to be barely warm so you can leave your hand on it forever doesn't seem right, now that I think about it.

But would that bias resistor affect the tube's performance and temperature ? Or just the bias measurement ?

Here's what I got:

Pin 4 optimum = 441
V5                      V4
P4 = 468            P4=467

Pin 5 optimum = -42
P5= -45.7             P5= -45.7

So voltages are all a bit high, but basically equal on the 2 tubes.

On pins 1 and 8 I get the same readings as the bias points.
The tube in V5 is barely warm while the tube in V4 is burning hot.

First Tube Swap Test
M1 is the Mesa and J1 is the JJ.

In the first configuration they're roughly balanced.
V5                             V4
M1=35.4                 J1=41.6

after swapping - grossly unbalanced
J1=26.5                  M1=51.5

So V4 is always higher and whichever tube is in there gets a lot hotter than V5.
Does that provide any clues ?