First pic of my 6V6 ODS build...finally fired it up!

[Bob-I]

Very nice looking build. I see from you're layout that you used Fender values on the plates/cathodes. I'm suprised too that it's hitting that hard. I built a 6V6 amp in the Princeton chassis using Dumble values, 220k/3.3k and 150K/2.2K.

So how effective is the tone stack? I find on mine that the treble is very subtle but the bass and mid are pretty effective.

BTW, I had some oscillation too. I needed to add some shielded wire to kill it.

[Normster]

It was getting late so I didn't mess with the tone stack. Just had everything at 12:00. I'll get some clips recorded this weekend, but my initial impression is that I missed the Deluxe Reverb tone by a mile. It sounds more like a Marshall.

[thejaf]

The "clone" I built 3 years ago hit really hard in the clean channel as you describe, and after I went throught the amp a second time I realized that the slope resistor actually had a faded orange stripe, and not the yellow stripe, so I was therefore off by a factor 10, hence the huge punch and less effective tone controls. It sounded good, so I kept it

Jeff

[Normster]

Real quick and dirty clip. Tele -> cable -> amp -> SM57. The reverb is a short tank, medium delay. I think I'm going to try a standard tank, long delay.

It definately needs some tweaking. The 25uF cathode caps have got to go. Great for Tele, suck for 335. I like the grit though. I think I'm going to make the snubbers switchable.

http://bad-domain/MP3/6V6ODSclip.mp3

[Bob-I]

Real quick and dirty clip. Tele -> cable -> amp -> SM57.

The ONLY way to record a clip

It definately needs some tweaking. The 25uF cathode caps have got to go. Great for Tele, suck for 335. I like the grit though. I think I'm going to make the snubbers switchable.

Before you trash the 25uF's add the snubbers and up the bright cap on the master. I'd bet you'll keep the snot in and smooth it out. I hear some boomyness that might be tamed with the bright cap, and some raspy high end that needs snubbers.

Great start Norm.

[Normster]

Doh, I didn't put a bright cap on the master yet.

I'll give that a shot as well as the snubbers. I think it's got lots of potential. Just needs some TLC.

[jelle]

Hi Normster,

Great build!

Maybe the silver mica treble cap is too sterile for this amp. I prefer ceramic for the higher gain amps.

I'd also add 270pf snubbers on OD1 and OD2.

How much volume difference do you get when the reverb section is disconnected? Maybe the reverb section is adding too much gain?

Just a thought,

Jelle

[Normster]

OK, here's the scoop...

Changed the 270pF Mica to a 270pF ceramic. By golly, you actually CAN hear a difference!
Changed the plate and cathode values to match #124 (from Gil's pics). IOW, 100k on the plates, 1.5k on the cathodes, with 10uF on CL1 & CL2 and 4.7uF on OD1 & OD2. I like it a lot! It's much tighter sounding now with humbuckers and still reasonably fat with the Tele.

I ended up with a 22pF bright cap on the Master. (Big surprise, eh Dogears?) I also changed the bright switch cap to a 270pF. Much more useable.

Finally, I added 270pF snubbers to OD1 & OD2 and put in the local feedback loop on CL2. It now sounds a lot more like a Dumble and a lot less like a Marshall.

For tubes I'm running EH12AX7's in V1 & V2, a JJ ECC83 in V3 (reverb) and a balanced triode JJ ECC83 in V4 (PI). Power tubes are EH 6V6's which are a tad brighter than the JJ's. Rectifier is a Ruby 5AR4.

Voltages:
B+1 = 374.5VDC (plate)
B+2 = 373.0VDC (screen)
B+3 = 366.0VDC (PI)
B+4 = 311.0VDC (reverb)
B+5 = 307.4VDC (OD)
B+6 = 301.8VDC (CL)

CL1 - 194.6 plate, 1.5 cathode
CL2 - 197.3 plate, 1.4 cathode
OD1 - 195.2 plate, 1.5 cathode
OD2 - 196.8 plate, 1.5 cathode
Reverb 293.6/183.5 plates, 2.0/1.7 cathodes
PI - 250.7/244.3 plates, 35.6/36.0 grid, 55.4 cathode
PA - 361.5 plates, 358 screens, -35.4 bias (25mA)

If my math is correct, it looks like 82-84% dissipation for V1 and 92-95% dissipation for V2.

OK, that's all the gory details I can think of at the moment. I'll get another clip recorded later.

[Bob-I]

Your voltages are MUCH lower than mine. I used a pair of Princeton replacement xformers and I'm getting far more voltage, I don't remember exactly but I think about 450 on the plates. I've heard that the JJ and EH 6V6's can handle this.

[Normster]

Your voltages are MUCH lower than mine. I used a pair of Princeton replacement xformers and I'm getting far more voltage, I don't remember exactly but I think about 450 on the plates. I've heard that the JJ and EH 6V6's can handle this.

Yup, that's the Trainwreck tranny with a 5AR4. HT is 300-0-300VAC. If I used a solid state rectifier I could bump it up to around 420, but the 5AR4 can only deliver about 375 max from this PT. It's got plenty of headroom so I think I'm OK.

Here's another clip after tweaking...
http://bad-domain/MP3/6V6ODSclip2.mp3

Same guitar, but I was trying out the loop with a bit of digital delay on this clip. The speaker is a 50W Sammi which is altogether wrong for this amp, but still not too bad. (It's perfect for the Trainwreck but has a little too much sizzle for an ODS.)

[jelle]

Hi Normster,

Now that's a nice tight clean sound! Totally different animal!

What values are you using for the NFB on V1b?

Thanks,

Jelle

[Bob-I]

Yes, I like the second clip better. You tend to run your gain lower than I do, I like to get it up to about 12:00 on the audio taper pot on both gains. I was thinking that it might be a bit spongy with the lower V1/V2 plate voltages, but I don't hear it.

I played with plate voltages on my 6V6 amp last. I'm still settled on 200V for V1/V2 as the best. Right now I'm at....

6V6 plates 440
screens 437
PI 307/298 cathodes 59
V2 195/202 cathodes 1.8/1.7
V1 199/203 cathodes 1.6/1.8

I raised it by removing the FET load resistor and it became quite harsh. When I went to put it back I broke a lead so I decided to try a 200K and lower the voltages. It became soft and spongy which I liked at first but after 30 minutes I decided it was too soft. I gotta get another 150K, that was my last. I put a 1W in for now but I calculated .8 watts, too close for comfort.


Great sounding amp Norm. Looks great too. What're you doing for a cabinet?

[Normster]

Thanks, Jelle! As much as I thought the "pre-tweak" version sounded kinda cool, I do like the post-tweak version much better. Many thanks to Gil for posting the info on #124...and of course to everyone else on this forum!!! Local feedback is 44M/.047uF.

Bob, our preamp voltages may be closer than you think. The first voltages I measured were 200.8/204.0 on V1 with old Chinese tubes. After putting in the EH's, it dropped about 10 volts. It's amazing how much the tubes effect operating voltages. When I settle on the tubes I like, I'll go back and tweak the dropping string a little. (I still want to try the JJ ECC803.)

For a cab, most likely another 1 x 12 combo. My friend Loren handles all the woodworking for me. I may try 3/4" 11-ply Baltic Birch for the cab and baffle this time.

As a side note, I see why Dumble uses 1/8" aluminum for his chassis. Compared to my other builds, this chassis has ZERO microphonics! When you tap on the chassis, you can't even hear it through the speaker. Anyone else using heavy aluminum notice this?

[Bob-I]

Bob, our preamp voltages may be closer than you think. The first voltages I measured were 200.8/204.0 on V1 with old Chinese tubes. After putting in the EH's, it dropped about 10 volts. It's amazing how much the tubes effect operating voltages. When I settle on the tubes I like, I'll go back and tweak the dropping string a little. (I still want to try the JJ ECC803.)

Yes, I've noticed the same thing. My tubes are a Sovtek 12AX7LPS in V1, EH 12AX7 V2 and JJ ECC83S PI, JJ 6V6's,

For a cab, most likely another 1 x 12 combo. My friend Loren handles all the woodworking for me. I may try 3/4" 11-ply Baltic Birch for the cab and baffle this time.

Has anyone tried a 1x10" combo? I like the idea of a Princeton sized Dumble combo.

As a side note, I see why Dumble uses 1/8" aluminum for his chassis. Compared to my other builds, this chassis has ZERO microphonics! When you tap on the chassis, you can't even hear it through the speaker. Anyone else using heavy aluminum notice this?

I actually think his main reason was strength. My 3 channel got pretty bent up in shipping.

[Normster]

I may a few more changes last night to bring the circuit closer to #124.
1. Replaced the Deep switch w/ Mid-boost. - I like it!
2. Changed Mid cap to .01uF. - Thumbs up.
3. Rewired Bright and R/J switches to match #124. - Check.

No surprise, but this switching arrangement works much better than the old style FOR #124's PREAMP VALUES. (Thought I'd emphasize that since Dogears is always reminding me it's a system. )

New layout with updates is here:
http://bad-domain/6V6_ODS/6V6_ODS_124.JPG

Visio if ya got it:
http://bad-domain/6V6_ODS/6V6_ODS_124.vsd