ODS Done - Clip with Strat and Clip with Hamer at Full Bore

[Luthierwnc]

BTW Drpastorbob, Do you shop at the black hole for some of his one-of-a-kind gadgets? He had a lot of Allen-Bradley carbon comp resistors in a big bin towards the back of the aisles. sh

[dogears]

Great clip! Nice tones and the playing was great. I kind of liked your tone a little more than the tone on my take over this backing. This about a 4 year old clip. I think it is the Fuchs 50. I may have multimiced. There is a little phasing on my clip.

http://scottlernermusic.com/music/Lowell.mp3

[drpastorbob]

Great clip! Nice tones and the playing was great. I kind of liked your tone a little more than the tone on my take over this backing. This about a 4 year old clip. I think it is the Fuchs 50. I may have multimiced. There is a little phasing on my clip.

http://scottlernermusic.com/music/Lowell.mp3

Scott,

Thanks for the compliment. It means alot coming from someone who plays as well as you do. I have listened to a lot of your clips and really enjoy your playing. I wish I had more time to practice and to learn some of the jazz scales. What you and I played over the same backing tracks is quite different - just goes to show that we all hear something different in our head. That's what makes playing music so much fun!

Blessings,

Bob

[drpastorbob]

BTW Drpastorbob, Do you shop at the black hole for some of his one-of-a-kind gadgets? He had a lot of Allen-Bradley carbon comp resistors in a big bin towards the back of the aisles. sh

Even though I have lived in Los Alamos for 20 years, I have only been there once and only recently with my buddy "RJGuitars" who goes there regularly. We were looking for capacitors. Lot's of stuff. I even may have recognized some equipment there from my grad school days. Quite the place!

[drpastorbob]

Sorry again - double post. The server is slow.

[drpastorbob]

My amp is based on the D'Lite diagram that I have attached - it's available elsewhere here on the forum. The amp is built as shown in the diagram with the exceptions listed below. I have also attached some photos of the outside and inside of the amp. Everything was built from scratch, not the D'Lite kit.

I am using:

1. Power Transformer = Heyboer PT-650-2, HTS-8816-2
325V-0-325V @225 mA

2. Output Transformer = Heyboer HTS-8603-2
4K Primary, 4/8/16 Ohm secondary taps
33 watts with 6L6s, 22 watts with 6V6s

3. Tubes
Power Tubes: Winged-C 6L6GC-0714 (2)
Preamp Tubes: Electro-Harmonix 12AX&EH (3)

4. Speaker = Eminence Legend 1218, 8 ohm

5. Lopo Large 12" open-back cab

Changes from the wiring diagram:

1. Dumble-style presence

2. PI Plates 110k/120K

3. OD Plates 220K/150K

7. 4.7K Feedback Resistor

8. 331 pF Treble cap / .02 uF midboost - Don't like the midboost much now.

9. 331 pF OD snubbers

10. Tube Voltages:
V1A = 186V
V1B = 191V
V2A = 225V
V2B = 174V
V3A = 293V
V3B = 292V

11. OD level = 20.8 kOhms (100K trim pot)

12. I have the two 22Mohm resistors that were in series with a capacitor across pins 6 & 7 of V1 removed.

That's it. Everything else is just as shown in the diagram. The pictures I took of the inside of the amp turned out somewhat out of focus. I'll post some better ones tomorrow when I have better lighting in the room. Midboost switch is on the back of the chassis, not the front.

Bob

Hey DrpastorBob:
Why don't you give us a brief tour of the amp. Plate and cathode resistors and caps. Entrance into the OD, loading of the OD level pot, tonestack values etc. You've got good balanced tone between single coils and humbuckers.

Dan

Dan,

I'd be more than happy to share all the details. Give me a couple of days and I'll verify all the values, summarize, and include pictures of the inside. I have not yet documented all the final values. This will force me to do so.

Bob

[drpastorbob]

Sorry server issues - double post

[dogears]

Hi Bob,

A few observations.

1) Your V2 cathode leads may be crossed. Check the size of V2a and V2b cathode resistors. Yoru voltages lead me to believe they are backwards.

2) Add a trimmer between PI plates. Your PI tube is so imbalanced you have more voltage on the feedback side. Your first triode should be higher than the second. Maybe swap tubes.... Shoot for about 5-6 volts more on the first half. Noticeable improvement in bass feel IMO.

3) The treble cap size has no effect on midboost. Just the cap size which is traditionally .002 and not .02 as you wrote. Try either .002/390pf or .001/470pf. You may prefer the .001/470pf as it gives you less extreme boost.

With the changes in place, try increasing the od trim to 30K or so....

Let me know. I think you'll dig them.

[drpastorbob]

Scott,

You were correct about the V2 voltages. I had the resistors reversed. Now the voltages are: V2A=199V, V2B=202V. I still need to check the midboost circuit and will have to get some other caps. I think I wired it up either/or .002/331 rather than the usual combination in series as you suggest. I'll change that. I have tried just a 470pF and that also sounded great.

Any ideas on tubes? As I said I am using EH 12AX7s, but have mullards, tung-sol, jj, etc. that I can also try. Any usefulness in using long-plates somewhere in the combination?

Also, can you explain to me why the the PI plate voltages should be different? As I said in previous posts, I am a very novice builder.

Thanks for all your previous suggestions.

Bob

Hi Bob,

A few observations.

1) Your V2 cathode leads may be crossed. Check the size of V2a and V2b cathode resistors. Yoru voltages lead me to believe they are backwards.

2) Add a trimmer between PI plates. Your PI tube is so imbalanced you have more voltage on the feedback side. Your first triode should be higher than the second. Maybe swap tubes.... Shoot for about 5-6 volts more on the first half. Noticeable improvement in bass feel IMO.

3) The treble cap size has no effect on midboost. Just the cap size which is traditionally .002 and not .02 as you wrote. Try either .002/390pf or .001/470pf. You may prefer the .001/470pf as it gives you less extreme boost.

With the changes in place, try increasing the od trim to 30K or so....

Let me know. I think you'll dig them.

[drpastorbob]

See the photos. I took the pictures today.

[Tonegeek]

Also, can you explain to me why the the PI plate voltages should be different? As I said in previous posts, I am a very novice builder.

one side of the PI has more losses than the other so you have to make that up which is why you see slightly different plate resistor values/voltages. Of course some people like the sound of an unbalanced waveform which you can attempt with the trimmer Scott referred to. There seems to be a sweet spot on the trimmer, but it is subtle IMO

[heisthl]

Scott is right it just "feels" better, somewhere between 3 and 7 volts difference you can find a spot where the 2nd order harmonics(octave above) are more prominent.

[drpastorbob]

Scott is right it just "feels" better, somewhere between 3 and 7 volts difference you can find a spot where the 2nd order harmonics(octave above) are more prominent.

Being a novice amp builder, could you guys please be a little more explicit for me - What value should the trimmer pot be, 10K, 100K? Also, I have poked around the files a bit and seem to have found only the HRM pictures. Anyone of you have the non-HRM circuit or pictures, or better yet the D'lite with the PI trimmer so I know how to wire it up?

Muchas Gracias,

Bob

[Tonegeek]

Scott is right it just "feels" better, somewhere between 3 and 7 volts difference you can find a spot where the 2nd order harmonics(octave above) are more prominent.

Being a novice amp builder, could you guys please be a little more explicit for me - What value should the trimmer pot be, 10K, 100K? Also, I have poked around the files a bit and seem to have found only the HRM pictures. Anyone of you have the non-HRM circuit or pictures, or better yet the D'lite with the PI trimmer so I know how to wire it up?

Muchas Gracias,

Bob

Most HRM and non-HRM schemos ive seen have the trimmer but not the D'lite. they all wire up the same way although some are 10k and others 5k. Take your pick. If you look in the files section at amp 124 schematic it uses a 5k pot between the plate resistors on the PI. It will be a challenge to work that into your existing circuit board but it could be done. I will say some people can't hear the difference with the trimmer. I feel like for me there was a sweet spot where as Heisthl pointed out, it gets slightly better harmonics. YMMV

[drpastorbob]

Hi All,

I tried a 10K trimmer and I can hear a region in the range where there seems to be more gain. I could not hear a change in the harmonics (aka sweet spot) so I set it for about a 5V difference between the two voltages. Since there is additional resistance now to both plates (common voltage into the wiper and the balanced voltages out to each plate through the same resitors as before), the overall plate voltages are lower: 282V, 287V. Should I have only used the Trimmer pot on one side so as not to reduce the overall voltages to the plates? I was at 293V and 292V before.

Bob