First Generation ODS #004 Just Wired Up

[67plexi]

Nice clean build David. I enjoy how you gave the amp your personal touch.

It will be interesting when you get your voltages squared away.

Keep us posted , Regards Steve.

[David Root]

Thanx Steve! I got the OD manual/pedal switch to operate the OD relay in manual, I had miswired the .1uF cap. Still working on the footswitch.

The OD needs work, I will probably change the exit to the OD MV to the second gen 1M/180K. It is putting out way more than the clean channel, glad I put in separate MVs.

[trane34]

Why two regulators? Very nice work...especially with drilling some straight holes.

[David Root]

Thanx! Only one regulator, 5V on the relay PS. The other TO-220 bottom left is the main PS rectifier, a dual diode 8A 1200V each.

Lots of holes indeed. Took a long time to do.

[Structo]

Nice build David!

Lots of goodies in there.

[David Root]

With Colossal's help I got the relay issues fixed. Thanx Dave!

First, I forgot to ground reference the relay PS board. I grounded the 5V regulator but not the rectifier bridge. Duh!

Then I connected the +ve leads from the footswitch to the relay board ahead of the coil/LED (yellow & white wires) instead of after it. See revised pic from Dave of this, and I also revised and reposted a correct gutshot.

Finally, after all this the 470R resistors in the footswitch box combined with the 150R already in the relay board choked off the feed to the coil, so I had to clip the body of the resistor out and solder the two leads together.

Now it works properly!

[David Root]

This 270K dropping resistor followed by the 9K2 before the 10K to the FET is just not working. Cannot make any sense of the schematic voltages on this first gen FET board.

I get 8.7V at the junction of the 270K/9K2/16K, schematic has 10.7V. I get 5.1V at the top of the 10K, schematic has 8.8V. I get 1.34V at the drain, vs schematic 6.5V(!). I get 1.27V at the source, vs. schematic at 0.78V.

Played with the 16K, up to 20K, and the 3K3 source resistor, down to 1K5. No joy.

Reduced the dropping resistor to 150K, this drops V1 & V2 a bit but still OK, they were a bit high to begin with. Still no sound out of the board.

Took out the 9K2 and jumpered it. No help.

Does anyone have any suggestions? Getting about 235V into the 270K. Schematic is 242V. This of course is a lot less than the 2nd gen FET board which is about 300V.

[crbowman]

Nice!!
I too have built a version of this circuit (albeit, with more readily available parts) and like it very much.
In regards to the OD entrance as published here:
https://tubeamparchive.com/viewtopic.ph ... 70&start=0
if you want to check it out, swap the 820K resistor with the 100K in the voltage divider feeding the OD circuit. Then you have 820K/100K voltage divider to 68k feeding V2A, and then 100K feeding the drive control. IMHO I feel this is probably the correct circuit.
When you lay it out, it's easy to see how the author of the schem transposed the two resistors. I've found this config makes the amp pretty much impossible to use as a true channel switcher, but if you just use it in overdrive it's really pretty sweet. Much more gain than the 2nd gen version. Tried adding a ratio control, but the OD seemed to loose something in the process.
Anyway, give it a shot if your curious.
And once again,
Nice build!

[ToneMerc]

Does anyone have any suggestions? Getting about 235V into the 270K..

David, now that I read this post, disregard my PM response.

Mike

[martin manning]

David I'm looking at the hand-drawn schematic for the FET. I see a 68k in series with the drain and a switch that looks like it must be an isolated "make" switch on the FET input jack. What did you do there?

[crbowman]

I never was able to sort out the FET circuit on this one.
Good luck!

[David Root]

Martin, I couldn't figure out what the switched 68K was for so I left it out.

crb, I'll persevere for a while, it's just a simple common source gain stage. Unless the schematic voltages are nuts you'd think it is possible to get Vd = Vcc/2 somehow.

Edit: Jumpered 9K2 again, changed 16K to 27K, 3K3 to 1K5, now getting 9V Vcc but only 1.3V at Vd. Vs is 1.0V, still no sound.

[martin manning]

So you have the 9k2 going from the 270k-16k divider directly to the junction of the 100uF and the 10k drain resistor? If so then I would put a pot in place of the 3k3 source resistor and dial up a point where the voltage drops by 50% across the 10k drain resistor. That should get some signal going through. If not then there must be something else wrong.

[David Root]

Martin, yes that's it, except I changed the 270K to 220K, which gives me exactly correct B+4 and B+5.

Unjumpered, the 9K2 in front of the 10K shows 13V at the divider but still too low at Vd. I'll try the 25K pot I have on Rs.

[David Root]

OK, I put my signal generator on the job and discovered that the FET jack only works if you pull the sig gen plug back about 1mm or so, then the +ve of the plug contacts with the right hand side of the jack. I've not had this problem with the 14B before. I bought six and have used two or three without problems.

Looks like I have been getting signal all the time but it's not getting thru the FET jack. The plug on my guitar cord has the same problem.

With my 25K pot in place of Rs, I can get 11.4V at the 220K/16K divider, 7.9V at the top of the 10K, 4.1V at the bottom (Vd), and 3.8V across the pot to ground, which measures 10K2 out of circuit. So 16K to ground works with Rs=10K2.

Since the 9K2 is in series with the 10K, shouldn't I be comparing the top of the 9K2 with the bottom of the 10K?

Now all I have to do is figure out how to fix the FET jack. I don't want to change it because a) that's a big job, have to remove both FET and NOR jacks as an assembly and b) since Switchcraft stopped making non-milspec jacks in the US the 14B probably has a 30% reject rate like the 12A does now.