ODS #183 Build

[ijedouglas]

Cool... So this (just redid it and added the extra eyelet).... 13K there on the dropping resistor. 100V bias tap.

Bias is good but your B+ rectification is wrong. Check the image I sent you again

The HT secondaries to go in the center (horizontal mid-line). Ground it at the top and B+ at the bottom.

[martin manning]

Looks good, if the under-board connections are like this:

[ijedouglas]

Looks good, if the under-board connections are like this:

PF-183_13.jpg

[pfarrell]

Yep... Under board connections are there!

[ijedouglas]

Yep... Under board connections are there!

Apologies

[pfarrell]

Zero worries...

Bolts ordered... what I have in stock have countersunk heads...

[pfarrell]

Some chassis holes and layout happened... waiting on the tranny bolts, hopefully tomorrow...then a pic! This is definitely a graduate level amp—lot's going on inside...

[Colossal]

This is definitely a graduate level amp—lot's going on inside...

10lbs of parts in a 5lb box!

[pfarrell]

Whoa. (bolts didn't show up... I went to the hardware store, bought what they had and cut them to length—old school ).
Definite insanity—no going back now.

PF-183_15.jpg

PF-183_14.jpg

[ijedouglas]

Whoa. (bolts didn't show up... I went to the hardware store, bought what they had and cut them to length—old school ).
Definite insanity—no going back now.

Is it done yet?

[pfarrell]

Ian, what's the theory behind not running the CTs to ground—since the PT has them? I've tested in other amps CT (if available) vs. the 100R resistors and the CT version was a tad quieter—though hard to tell in practicality—i was under the impression if the PT has them—use them for quietest results—Fender's though......Also, anyone have some clarity about all the different grounding points in theory on the Dumble...? I'm not sure how Martin's eyelet board labels match up with actual ground layout in the amp—the layout file I have isn't too clear, don't want to inadvertently make any loops...

[ijedouglas]

Ian, what's the theory behind not running the CTs to ground—since the PT has them? I've tested in other amps CT (if available) vs. the 100R resistors and the CT version was a tad quieter—though hard to tell in practicality—i was under the impression if the PT has them—use them for quietest results—Fender's though......Also, anyone have some clarity about all the different grounding points in theory on the Dumble...? I'm not sure how Martin's eyelet board labels match up with actual ground layout in the amp—the layout file I have isn't too clear, don't want to inadvertently make any loops...

Sorry, only saw this now.

I don't know if I have heard any difference but from what I've read, the 100R balance resistors are supposed to be quieter AND could potentially save your transformer (the 100R acts like a fuse). Not sure I want to rely on that to save my transformer but I guess it can't hurt (unless you hear a difference)

I use the grounding scheme on the 183 layout and it works pretty well. Not sure how/if it differs from Martin's eyelet boards. I also clean (with a Dremel) all the pot holes, jack holes and ground locations. I have the AN chassis and although they are masked during powder coating, you would be surprised at the difference when checking resistance between ground points (maybe the video of Ben Harper talking about HAD testing the chassis with probes was referring to this).

[martin manning]

Also, anyone have some clarity about all the different grounding points in theory on the Dumble...? I'm not sure how Martin's eyelet board labels match up with actual ground layout in the amp—the layout file I have isn't too clear, don't want to inadvertently make any loops...

Refer to the #124 schematic here: https://ampgarage.com/forum/viewtopic.p ... 006#p55006, where five chassis ground points are identified.

The corresponding eyelet board ground connections are as follows [edited to include all chassis ground points]:

1 - Input jack ground - Preamp board V1 and V2 cathodes, main power supply board preamp filter capacitors (B+4 and B+5), FET board filter capacitor (B+6) and FET source, input jacks, preamp bus, OD input ground on OD relay
a - Loop jack ground - Preamp board V3 cathodes
b - Speaker jack ground - OT secondary common
2 - Power tube cathode V4,5 ground - Main power supply board screen and PI filter capacitors (B+2 and B+3), heater string ground reference resistors (if present)
a - Bias trimmer ground - rectifier/bias supply board bias supply filter capacitors
3 - Power tube cathode V6,7 ground -
4 - HT ground - Main power supply board reservoir capacitor (B+1), HT CT (two phase rectifier) or rectifier/bias supply board negative (bridge rectifier)
5 - Relay supply ground - Relay supply board filter capacitors and regulator, foot switch jack

[ijedouglas]

Also, anyone have some clarity about all the different grounding points in theory on the Dumble...? I'm not sure how Martin's eyelet board labels match up with actual ground layout in the amp—the layout file I have isn't too clear, don't want to inadvertently make any loops...

Refer to the #124 schematic here: https://ampgarage.com/forum/viewtopic.p ... 006#p55006, where five chassis ground points are identified.

I think there is a slight difference in the power supply grounding between the 183 and 124. 124 has the screens and PI filters grounded together at ground between V4 & V5. 183 has screens grounded at ground between V4 & V5 and PI/V2/V1 filters grounded at the input jack.

[martin manning]

I think there is a slight difference in the power supply grounding between the 183 and 124...

True, but either way will work just fine. The the main power supply board pattern Pfarrell is using has B+2 and B+3 grounds merged and routed to be grounded with the power tube cathodes.