I thought I would document my journey building my first ODS amp. Since I have a JM signature (classic stack), I thought i would try a High Plate Skyliner first, based on the Robben Ford ODS #0102 but with some liberties here and there based on parts I could source. I am using the #124 pictures as a lead dress reference. Thanks to everyone that has contributed here over the years, I appreciate the sharing of information so much and willingness to help others. I tried my hardest to get period correct parts where possible, though it is pretty tough these days. Big thanks to Taylor for the chassis and boards, Jelle for most of the dralorics, the orange drops, and other odds and ends.
Here is the chassis with hardware loaded up. Volume and Master pots are modern 1M J taper CTS from Jelle. Presence pot is 2K modern Alpha. Treble and Middle pots are 250K NOS CTS from 1961. Bass is 500K NOS Clarostat from 1966. Level pot is 100K NOS Centralab from 1972 and Ratio pot is 100K NOS Centralab from 1976. Bias pot is modern CTS.
Relay transformer is Hammond 166G6.
Quick question, on Martin's board files I see most of the time the PI filter cap is grounded with V1 and V2. But on all of the ODS layouts, it looks like the PI filter is grounded with the Screen filter. I am leaning towards keeping it with the screens, any pros or cons of either approach?
-Dan
NOS #102 Build
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NOS #102 Build
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ijedouglas
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Re: NOS #102 Build
#0124 was grounded with the screens. Other amps with the precision power supply had the PI grounded with V1 + V2. I'm sure it makes a difference although I don't think it is significant. I would just do it as HAD did itdbharris wrote: ↑Sun Jun 04, 2023 7:00 pm Quick question, on Martin's board files I see most of the time the PI filter cap is grounded with V1 and V2. But on all of the ODS layouts, it looks like the PI filter is grounded with the Screen filter. I am leaning towards keeping it with the screens, any pros or cons of either approach?
Ian
Re: NOS #102 Build
Thanks! I am doing the traditional power supply, I will tie the PI ground with the Screens.ijedouglas wrote: ↑Sun Jun 04, 2023 7:52 pm#0124 was grounded with the screens. Other amps with the precision power supply had the PI grounded with V1 + V2. I'm sure it makes a difference although I don't think it is significant. I would just do it as HAD did itdbharris wrote: ↑Sun Jun 04, 2023 7:00 pm Quick question, on Martin's board files I see most of the time the PI filter cap is grounded with V1 and V2. But on all of the ODS layouts, it looks like the PI filter is grounded with the Screen filter. I am leaning towards keeping it with the screens, any pros or cons of either approach?
-Dan
Re: NOS #102 Build
Making slow progress as time permits. What do you guys think about screen resistors? I have some 560 ohm dralorics on hand or I could order some 470 ohm iskras. Do you think the larger resistance will roll off too much high end?
FET Board before I biased it up and swapped 1 resistor. Using a 2n5457:
Power Supply Board is done as well. I did have to put a 20k and 2k2 in series:
Relay Power supply and Transformer in...working my around the chassis for odds and ends that can be wired in before the main board:
-Dan
FET Board before I biased it up and swapped 1 resistor. Using a 2n5457:
Power Supply Board is done as well. I did have to put a 20k and 2k2 in series:
Relay Power supply and Transformer in...working my around the chassis for odds and ends that can be wired in before the main board:
-Dan
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Re: NOS #102 Build
A little more progress. Snubbers and some other parts (will show up in the future) generously donated by another TAG member. Massive thanks to him!
-Dan
-Dan
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Re: NOS #102 Build
Been busy with work, life, and went to see Dead & Co at the Gorge. Getting back into the swing of things now. Have most of the chassis wired up and built the main board today. PT and Bias boards next.
-Dan
-Dan
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Re: NOS #102 Build
Awesome!
That kind of build sounds like the challenge of a whole life, these days. I can't imagine for how long you've been gathering all the parts for this build ...
That kind of build sounds like the challenge of a whole life, these days. I can't imagine for how long you've been gathering all the parts for this build ...
Re: NOS #102 Build
Quite a while haha. It's part of the fun but I do wish a stash of the good parts would just appear sometimes! I've been fortunate to have several members here sell or gift me certain parts. TAG is the best online community IMHO.
-Dan
Re: NOS #102 Build
Just have heaters left, then smoke test and burn in.
-Dan
-Dan
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Re: NOS #102 Build
Choke and PT are new Amp Parts Direct x Heyboer. I finished wiring the heaters and made some final adjustments to lead dress before firing up. Running through the startup procedure now and forming caps. Unfortunately I have to go out of town this afternoon for the night so I may not get to hear the beast until Sunday night or Monday.
-Dan
-Dan
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ijedouglas
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1 others liked this
Re: NOS #102 Build
Mostly good so far. I had wired one half of the LED indicator power supply wrong. Moved that wire and all good.
Fired up with JJ power tubes and new mullard noval tubes. Voltages are all in the ball park except my B+ is a little low at 423V with the tubes biased. These are just the tubes to test out initially so I am not really focused on that yet. My PT is 320-0-320 and I thought that was loaded, but maybe it is unloaded? Seems like my OT leads are correct.
Amp is passing signal and clean sounds about like I would expect. Something is off with the overdrive, even with the trigger maxed out the volume is lower than the clean channel. Will spend some time on that when I can reflowing joints and maybe signal tracing with the scope.
Roughly set the PI trimmer by ear but again, I am going to swap out all of the tubes soon.
FET is not passing signal. Need to investigate further, I may have fried the FET when swapping bias resistors or maybe some other silly error with wiring the jacks.
Also need to build the footswitch.
-Dan
Fired up with JJ power tubes and new mullard noval tubes. Voltages are all in the ball park except my B+ is a little low at 423V with the tubes biased. These are just the tubes to test out initially so I am not really focused on that yet. My PT is 320-0-320 and I thought that was loaded, but maybe it is unloaded? Seems like my OT leads are correct.
Amp is passing signal and clean sounds about like I would expect. Something is off with the overdrive, even with the trigger maxed out the volume is lower than the clean channel. Will spend some time on that when I can reflowing joints and maybe signal tracing with the scope.
Roughly set the PI trimmer by ear but again, I am going to swap out all of the tubes soon.
FET is not passing signal. Need to investigate further, I may have fried the FET when swapping bias resistors or maybe some other silly error with wiring the jacks.
Also need to build the footswitch.
-Dan
Re: NOS #102 Build
Hi Dan,dbharris wrote: ↑Mon Aug 21, 2023 2:37 pm Mostly good so far. I had wired one half of the LED indicator power supply wrong. Moved that wire and all good.
Fired up with JJ power tubes and new mullard noval tubes. Voltages are all in the ball park except my B+ is a little low at 423V with the tubes biased. These are just the tubes to test out initially so I am not really focused on that yet. My PT is 320-0-320 and I thought that was loaded, but maybe it is unloaded? Seems like my OT leads are correct.
Amp is passing signal and clean sounds about like I would expect. Something is off with the overdrive, even with the trigger maxed out the volume is lower than the clean channel. Will spend some time on that when I can reflowing joints and maybe signal tracing with the scope.
Roughly set the PI trimmer by ear but again, I am going to swap out all of the tubes soon.
FET is not passing signal. Need to investigate further, I may have fried the FET when swapping bias resistors or maybe some other silly error with wiring the jacks.
Also need to build the footswitch.
-Dan
If your FET is defective your B+ voltages will be slightly lower.
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martin manning
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Re: NOS #102 Build
Unless it's open, in which case they would be slightly higher.
I would measure the voltages at the top and bottom of the 10k drain resistor to see if it is biased correctly, drawing about 1 mA.
Re: NOS #102 Build
Correct, the 423v is too low. I had this with my 2nd gen hybrid. Defective FET; lower voltage. B+ should be around 440v with his secondary taps.martin manning wrote: ↑Mon Aug 21, 2023 3:53 pmUnless it's open, in which case they would be slightly higher.
I would measure the voltages at the top and bottom of the 10k drain resistor to see if it is biased correctly, drawing about 1 mA.
But the possibilty something else is off remains.