Raoul Duke wrote: ↑Sun Nov 26, 2023 9:27 pm
Been comparing the power sections of the 102 layout and the 3rd gen ODS layout trying to figure out what to mix and match to get the 50w 102. Commonalities I see are the artificial CT, PIN 8 grounded, the 470r screen resistor (although they are mounted differently - one to pin 6, one to a terminal strip) and different value grid stoppers from pin 5 to either pin 6 or pin 1.
Uncommon parts are the aforementioned “2nd pins” above and tying pins 6 and/or pins 3 - which both look like 100w specific connections to sync pairs and tie the OT primaries (as a guess).
I understand that they are two different designs, but figured I’d start there. My aim is to wire-up the power section to test as much as possible before diving into the main board (read about Marcus doing that on his first build as recommended by Martin). I prefer to test things as I go vs when going through power up if at all possible - so any guidance to that end is appreciated!
In all the pics I have of 2nd/3rd Gen amps, the pin/component layout is the same as the layout on the #0102 layout which is the layout I prefer. You are just using unused pins (1 and 6) as tie-off points.
Ok, thanks Ian!
So the grid stoppers to 1 & 5 are ok and screen grids to 4 & 6 are ok then? I used the values in the 102 layout but the stoppers in the 50w are 2k2 - which I’m thinking is correct for the Bassman spec iron I’m using (vs the 100w spec iron in the 102 layout)?
So looking at Tony’s 2/3rd gen power sections - would I be able to just copy those (but using Martin’s power board and the pin 1&6 tie-off points vs terminal strips) and add the LED terminal strip next to V5?
Thanks again! Hopefully my questions aren’t too annoying. I’m really learning an awful lot and trying to read everything I can on these subjects so that I’m formulating my thoughts in a logical way, lol…
Raoul Duke wrote: ↑Mon Nov 27, 2023 2:12 am
So the grid stoppers to 1 & 5 are ok and screen grids to 4 & 6 are ok then? I used the values in the 102 layout but the stoppers in the 50w are 2k2 - which I’m thinking is correct for the Bassman spec iron I’m using (vs the 100w spec iron in the 102 layout)?
Yes and yes. I think for my #0102 I used 5K1. I would stick with the values for the #0102 but once you have the amp up and running you can certainly experiment with 2K2.
Raoul Duke wrote: ↑Mon Nov 27, 2023 2:12 am
So looking at Tony’s 2/3rd gen power sections - would I be able to just copy those (but using Martin’s power board and the pin 1&6 tie-off points vs terminal strips) and add the LED terminal strip next to V5?
I'm not quite sure what LED terminal strip you are referring to? Is that the diode and dropper coming off the heaters to power the LED? If so, I would put it between V5 and where V6 would have been (so the same as where it would be with the #0102 layout)
Yes, the diode and dropper - and it’s already in your suggested location, so we’re good there.
Hopefully I’ll get some opinions regarding copying the 2/3 gen power section as well.
I meant regarding the layout of the 2/3 gen power section and copying it directly. I’ve been trying to trace each connection and for the most part they seem pretty similar; just not entirely sure based on my lack of understanding the many nuances to circuit design.
Not looking for second opinions on your always great advice - I hope it didn’t sound that way. Certainly not my intent.
Raoul Duke wrote: ↑Mon Nov 27, 2023 1:20 pm
I meant regarding the layout of the 2/3 gen power section and copying it directly. I’ve been trying to trace each connection and for the most part they seem pretty similar; just not entirely sure based on my lack of understanding the many nuances to circuit design.
Not looking for second opinions on your always great advice - I hope it didn’t sound that way. Certainly not my intent.
I would seriously recommend sticking with the #0102 power section (except for 50W) which means everything except the PT/OT and only 2 power tubes. I think just about everything else stays the same. I would even try and stick to the dropping resistor values. You may need to adjust the 1st dropper (2k7) to get in the ballpark. HAD was pretty consistent with his droppers and I think he was using them as filters/separation between nodes rather than to tweak the node voltages. I would start out with 2K7 => 22K => 2K2 and then adjust the 2K7 to 2K2 i your voltages are too low. Try and shoot for 190-200 on V1 and around 200-210 on V2. IMO tubes make a bigger deference to your voltages than the droppers. You really only need to worry about this once the amp is up and running.
Remember, 2nd/3rd Gen amps are a totally different circuit and will have a different outcome. The high-plate skyline evolved from those earlier models and HAD adjusted values as he experimented and furthered his knowledge.
Makes sense - thanks Ian. That’s exactly what I was wondering (about the difference).
So I should focus on 102 V4 and V6 wiring and eliminate the OPT connections that link 4 to 5 and 6 to 7 (pins 3) - but keep the link at pins 6 going on to B+2? Correct?
After reading a bunch of other build threads and looking at pictures combined with Ian’s guidance (thanks again for your patience Ian) - I think I have the power section figured out. I’ve written out where everything will go from PT, OT, choke, and relay trans as well as the power tube connections and PS board - which helps me understand. The questions I have left are:
1. regarding the HV CT (red/yellow): my understanding is that it would go to ground?
2. the 5v rectifier windings (yellow): do I clip and cap those or do they go to ground as well?
It’s funny how I stare at this stuff and try and figure it out for days - then one or two explanations from the seasoned veterans here combined with some more “search” time and it suddenly falls into place. Great education I’m getting
Raoul Duke wrote: ↑Tue Nov 28, 2023 12:26 am
After reading a bunch of other build threads and looking at pictures combined with Ian’s guidance (thanks again for your patience Ian) - I think I have the power section figured out. I’ve written out where everything will go from PT, OT, choke, and relay trans as well as the power tube connections and PS board - which helps me understand. The questions I have left are:
1. regarding the HV CT (red/yellow): my understanding is that it would go to ground?
2. the 5v rectifier windings (yellow): do I clip and cap those or do they go to ground as well?
It’s funny how I stare at this stuff and try and figure it out for days - then one or two explanations from the seasoned veterans here combined with some more “search” time and it suddenly falls into place. Great education I’m getting
Thanks all - very much appreciated!
1. Yes
2. You can use those instead of a separate relay transformer. Otherwise add some heat shrink to the ends so they can't shirt and tie them off but don't connect to ground.
If your PT has a heater center tap, you would not connect it to ground either, just heat shrink the end and tie it off.
All that being the case - here’s today’s update pic. PT, OT, and choke installed. Had to shift the OT slightly to the right to clear some board mounting screws; maybe 3/8”. Started getting the PT ready for wiring and did my research/creative writing exercise, lol.
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Raoul Duke wrote: ↑Tue Nov 28, 2023 12:26 am
1. regarding the HV CT (red/yellow): my understanding is that it would go to ground?
Not just any ground, it has to go to the first filter/reservoir ground, near the bias/rectifier board. See layout drawing.
Raoul Duke wrote: ↑Tue Nov 28, 2023 12:26 am
2. the 5v rectifier windings (yellow): do I clip and cap those or do they go to ground as well?
Do not ground them. Clip or coil and cap the ends with heat shrink. You can use the 5V winding for the relays, but only if your relay supply rectifier is a doubler and you are using 5V relays.
More progress. Got the impedance switch wired, started prepping for the PT connections, and semi-wired the IEC/fuse/mains switch. I think I understood the wiring correctly, but haven’t heated anything on the mains switch pending a second set of eyes (or more, lol). Had to lengthen the relay transformer leads to get them tucked back where I wanted them (blue/black).
Got some parts today and will re-try FET bias tomorrow. Will report back with results.
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Raoul Duke wrote: ↑Sat Dec 02, 2023 1:30 am
More progress. Got the impedance switch wired, started prepping for the PT connections, and semi-wired the IEC/fuse/mains switch. I think I understood the wiring correctly, but haven’t heated anything on the mains switch pending a second set of eyes (or more, lol). Had to lengthen the relay transformer leads to get them tucked back where I wanted them (blue/black).
Got some parts today and will re-try FET bias tomorrow. Will report back with results.
Looks good to me.
For future reference, I normally leave the PT till the very last. It's heavy and there is no need to take on extra weight until the very last minute (wiring the heaters in my case). I also leave the OT out until I'm pretty much ready to mount the preamp board.
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