ODS - Cabinet Finished - First Gig - Still Tweaking

[RJ Guitars]

I finished up my ODS combo cabinet and played my regular Sunday gig within 12 hours of putting the final screws in the back.

This amp has the very best clean tone of any amp in my arsenal... I can't say too much about the OD channel yet, I'm still figuring out how to use it. I did find that I'm getting the most "Dumble like sound" with the OD trimmer pot squeezed down to provide minimal overdrive. I get a buzzy unpleasant distortion if I crank up the trimmer.

I'm waiting on a parts order that includes the essential resistors to move the voltages around in the power supply dropping string in order to get:
200 V1 -
200 V2 -
290 V3 -
445 V4/V5 -

This is the perfect formula as far as I can interpret things.... let me know if I'm way off base. Right now my phase inverter is pretty hot at 335V, but my V1 & V2 are pretty close to 200V. My V4/V5 voltages are 447V right now.

Does anybody see any issues with my cabinet layout? I didn't intend to have that knot hole at the top of the speaker opening, but it turned out I moved the speaker down lower than I had originally planned to adequately clear the OPT. I went with cheap pine and simple construction since I want to gig with this amp and I know I'd beat up a really nice cabinet. Eventually I'll either tolex it or coat it with something like the spray-on bed liners for trucks. (I'll work on a better front panel photo and edit in in later).

The speaker is an EV (thanks to Zippy on this forum). I don't know much about the speaker, except it does sound really nice.

I'm greatly appreciative of the forum for all the good info they have provided.

rj

[nickt]

Looks pretty darn good!

I'm a big EV fan - got one that's been going strong since 1979 - maybe a backup would be nice Best speaker ever made IMNSHO

Still tossing up whether to go combo or head+cab for my D'lite

cheers
Nick

[stelligan]

I only have one issue with the cabinet - it's not in my music room Looks very nice.

Nicely done. You will not go wrong with that speaker.

[heisthl]

Nice cab - forget about spary on bedliner though, I got all excited about DupliColor selling spray cans of bedliner till I tried it. It is no way near durable enough unless you like constant messy touchups. What might work is rolled on fibreglas but that would be really hard to do in the inside corners. Just put one of those signs on the front that says "This is a natural product and the scuffs and scratches add to it's natural beauty", or brush up on yout tolex skills.

[Structo]

Nice job!
Which EV speaker did you use.
I wonder how you got 447v on the power tubes?
The PT is 325v.
I think my power tubes are 430v at the plates.
What is the house current voltage in your area?

Try lowering your choke resistor to 300-330 then check your tube voltages.
I changed the V4,5 screens to 470R and the grids to 3K3.
I changed my PI Rp to 120K/110K.

[Pete]

Looks like a great amp. I've giged for many years with basically the same thing, very heavy unit, especially with the EV. I'm currently in the process of changing over to head & 1X12 cab. The cab is very light and I will probably be going with G12-65. I'm not as young as I use to be.

As for your voltages, everything looks pretty good (IMHO), PI maybe a bit on the high side but over 300 to 318 or so is not uncommon for a typical non BM build. Maybe try a different 12AX7.
Glad you are enjoying your amp.

[RevD]

Looks really good, the only thing I'd do different and this is put a oval slot where the tubes are for a bit more ventilation. Perhaps this is a bit nit picky but I think the valves might stay happier longer, just an opinion though.

Regards,

Rev.D

[dogears]

Some suggestions:

1) Change PI plates to 110K/120K as suggested already
2) Change OD plates to 220K/150K along with appropriate cathode resistors
3) No bright cap or 10pf at most
4) 4.7K feedback resistor for power amp feedback
5) .01uf midcap and 250ka midpot
6) 330pf treble cap
7) 330pf snubbers
8 ) 300K (500k trimmer is even better) and .001uf cap to ground from OD2 plate if OD is still buzzy
9) Is there shielded on OD pots? All 4 connections
10) series .05uf cap before the pre OD network (the 220K resistor), use 4.7m to ground to keep from popping

[RJ Guitars]

Nice job!
Which EV speaker did you use.
I wonder how you got 447v on the power tubes?
The PT is 325v.
I think my power tubes are 430v at the plates.
What is the house current voltage in your area?

Try lowering your choke resistor to 300-330 then check your tube voltages.
I changed the V4,5 screens to 470R and the grids to 3K3.
I changed my PI Rp to 120K/110K.

I really don't know anything about the speaker except that it's an EV... I picked up as a loaner from another local builder. There are some numbers on the back but I haven't dug in to try and I.D. it.

My Local AC voltage is 117V. My PT is an old Stancor unit. It is 337.5-0-337.5, however, I have a 13 volt Zener on it to drop it to 324.5V AC.

I just ordered a bunch of alternate resistor values to start implementing a bunch of the suggested mods.

Thanks very much for the good input!

rj

[RJ Guitars]

Some suggestions:

1) Change PI plates to 110K/120K as suggested already
2) Change OD plates to 220K/150K along with appropriate cathode resistors
3) No bright cap or 10pf at most
4) 4.7K feedback resistor for power amp feedback
5) .01uf midcap and 250ka midpot
6) 330pf treble cap
7) 330pf snubbers
8 ) 300K (500k trimmer is even better) and .001uf cap to ground from OD2 plate if OD is still buzzy
9) Is there shielded on OD pots? All 4 connections
10) series .05uf cap before the pre OD network (the 220K resistor), use 4.7m to ground to keep from popping

Dogears I am so pleased that you jumped in here and gave me all the tweaks in one post! I intend to try all of them, although I'll implement them one at a time. It's amazing to me that you have accurately identified most of the "Needs Improvement" areas on an amp you haven't heard yet, and have a suggested fix... thanks!

Just to remove any doubt that I'm a novice builder, would you share those appropriate cathode resistor values with me that you mention in item 2)? As I look at the schematics, I see the 220K/150K plate resistors with a 3.3K and a 2.2K respectively... is that correct or does that simply prove that I am altogether ignorant?

Thanks, I am greatly appreciative that you'll share your expertise...

rj

[gregarious]

I dig the way you "grilled" the speaker baffle!

Nice lookin' cab - trust it's deliverin' the goods!

[dave g]

That is correct, the 220/150 go with 3.3/2.2 - in both cases it preserves the ~67:1 ratio

[markmalin]

Some suggestions:

7) 330pf snubbers
8 ) 300K (500k trimmer is even better) and .001uf cap to ground from OD2 plate if OD is still buzzy

Just to help me understand this, can I ask 2 questions?

- #7 What effect does going from 270pf to 330pf snubbers have?
- #8 I haven't seen anything about this mod. Can you explain it? My OD is buzzy, too, so I'm considering trying this.

TIA
Mark.

[markmalin]

I finished up my ODS combo cabinet and played my regular Sunday gig within 12 hours of putting the final screws in the back.

Nice looking amp, RJ! What output transformer did you use? Are those 6L6's?

Thanks,
Mark.

[RJ Guitars]

I've had a ton of questions to follow up with on this thread... some of them I've answered in other posts as I built this amp.

I thought it might be useful to have a link to every post in one easy to find spot... so here they are. Let me know if this useful or violently offensive...

rj

Verifying some cabinet dimensions:
https://tubeamparchive.com/viewtopic.ph ... ght=#43715

When I first finished my amp - it sounded awful
https://tubeamparchive.com/viewtopic.ph ... ght=#43282

I did a few things different
https://tubeamparchive.com/viewtopic.ph ... ght=#43059

The earliest stages of this amp - lots of chassis and faceplate info
https://tubeamparchive.com/viewtopic.ph ... ght=#42442

A query about the ideal tube compliment for an ODS
https://tubeamparchive.com/viewtopic.ph ... ght=#41831

Clearing up a little of my confusion on output tube wiring
https://tubeamparchive.com/viewtopic.ph ... ght=#40695


A post by another local builder - very similar amp build
https://tubeamparchive.com/viewtopic.php?t=4343

A 2nd Thread on the DrPastorBob Amp
https://tubeamparchive.com/viewtopic.ph ... highlight=