Hello all! I'm new to the forum today.I'm a 50 yr. old retired fart and have amp buiding experience back to the 60's and hope I can contribute as well as gain info from you all.I plan to build my first 18 watter and use a Fender Pro Jr cab and Hammond chassis I have.I have all the parts I need including board and turret lugs and now I'm just needing a layout for a lite version with just a single volume and tone control.Is there a scaled drawing of layout for just the turret board or do I just need to draw my own?Thanks!Board Layout for Pro Jr.
Moderators: zaphod_phil, Daviedawg, Graydon, CurtissRobin, colossal
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Putter
Board Layout for Pro Jr.
Hello all! I'm new to the forum today.I'm a 50 yr. old retired fart and have amp buiding experience back to the 60's and hope I can contribute as well as gain info from you all.I plan to build my first 18 watter and use a Fender Pro Jr cab and Hammond chassis I have.I have all the parts I need including board and turret lugs and now I'm just needing a layout for a lite version with just a single volume and tone control.Is there a scaled drawing of layout for just the turret board or do I just need to draw my own?Thanks!
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Attilio
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http://voodoochild.altervista.org/immagini/lite.jpg
Et voila!
Before building your amp check the layout comparing it with the schematic. Anyway it should be correct.
Bye!
Attilio
Admins please read:
If my layout is correct is possible to add it in the layouts download page?
Thanks!
Et voila!
Before building your amp check the layout comparing it with the schematic. Anyway it should be correct.
Bye!
Attilio
Admins please read:
If my layout is correct is possible to add it in the layouts download page?
Thanks!
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markh
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Just teasing - any picture is still worth a thousand words!
) yesterday, and I have to re-install my graphic softwares... when I do it I will modify my layout and post a correct version.-
Wrongdog
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Lite schematic question
How come I see the resistor to pin 1 of the V2 sometimes being 100k and others being 82k. What gives??
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markh
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The Schmitt PI that so many amps use (including this one) is inherently slightly imbalanced. If you use identical plates resistors on both sides, the two outputs will not be equal in amplitude, and this causes a little harmonic distortion.
If you're using both sides of the PI as inputs (as does the original 18watt circuit), you have to "live with it." If you're only using one input to the PI, you can correct for this by making the non-input side plate resistor slightly smaller. The closest standard 5% value to properly complement 100K is 91K, but back in the day when this was first done, 10% tolerance resistors were the rule, and the closest standard value was 82K. So, even though 82K is not ideal, it is better than 100K, and was used in many classic circuits, including the Bassman and Plexi circuits.
If you're doing a lite varient:
- If you want the cleanest clean sound, use 91K
- If you want the most authentic sound to the original, use 100K.
- If you like tradition, use 82K.
All will work, and the difference in sound will be very subtle.
--mark
If you're using both sides of the PI as inputs (as does the original 18watt circuit), you have to "live with it." If you're only using one input to the PI, you can correct for this by making the non-input side plate resistor slightly smaller. The closest standard 5% value to properly complement 100K is 91K, but back in the day when this was first done, 10% tolerance resistors were the rule, and the closest standard value was 82K. So, even though 82K is not ideal, it is better than 100K, and was used in many classic circuits, including the Bassman and Plexi circuits.
If you're doing a lite varient:
- If you want the cleanest clean sound, use 91K
- If you want the most authentic sound to the original, use 100K.
- If you like tradition, use 82K.
All will work, and the difference in sound will be very subtle.
--mark
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Wrongdog
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Wrongdog
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Please excuse my ignorance but as a newbie I will have some dumb questions for you all - thanks for your patience!
My hifi Grommes conversion to the 18 watter ("the Gomer Pyle Driver" as I call it, born Sat. 5/10/03) works and sounds great after one minor debug. That is except for the one tube plate that slightly glows. I don't have the voltages with me here at work but they all were 5-7% higher than what most of the discussions seemed to indicate as optimal. I will check them all but I went with the 100K rather than the 820K at pin one as I had asked about earlier. Would that affect the power tubes? Only the one socket goes red and swapping tubes (RCA blackplates) made no difference. That resistor would only affect the preamp, right??
BTW I am using an EZ80 and temporarly the original OT, PT and 40/30/20 cap can. I know that sounds nuts what with being 40 years old but the amp was and is stone quiet. It was used regularly and is hum free. I am ordering new caps from Antique Electronics this week. The rest of the amp is exactly to the schematic.
Is there a universal color code to the old output tranny impedences? Is orange 16, green 8, yellow 4 etc?? The Grommes is a Mohawk. Is Niagra-Mohawk the same company??
My hifi Grommes conversion to the 18 watter ("the Gomer Pyle Driver" as I call it, born Sat. 5/10/03) works and sounds great after one minor debug. That is except for the one tube plate that slightly glows. I don't have the voltages with me here at work but they all were 5-7% higher than what most of the discussions seemed to indicate as optimal. I will check them all but I went with the 100K rather than the 820K at pin one as I had asked about earlier. Would that affect the power tubes? Only the one socket goes red and swapping tubes (RCA blackplates) made no difference. That resistor would only affect the preamp, right??
BTW I am using an EZ80 and temporarly the original OT, PT and 40/30/20 cap can. I know that sounds nuts what with being 40 years old but the amp was and is stone quiet. It was used regularly and is hum free. I am ordering new caps from Antique Electronics this week. The rest of the amp is exactly to the schematic.
Is there a universal color code to the old output tranny impedences? Is orange 16, green 8, yellow 4 etc?? The Grommes is a Mohawk. Is Niagra-Mohawk the same company??
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markh
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If you're using shared cathode bias (as in the original) and the redplate symtom does not move with the tube, I'd check all the connections around the suspect tube socket. Do the grids and cathodes on both output tubes measure the same? Try switching out (or swappng if you have no spares) the two coupling caps feeding the two output tube grids.
--mark
--mark
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Wrongdog
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Mark, thanks.
I replaced them to no avail, I touched up all solder joints etc. I am still redplating very slightly on the one tube socket but noticed that swapping the 2 tubes one is less red now. It is very slight in both tubes at the V4 EL84 socket with lights out. I think I am right at the threshold of the old RCA's and will put a 10 watt resistor in series at the 130 cathode bias resistor and knock it down just a tad. I have dropped voltages ever so slightly?? I did have a dirty tube socket on the non-redplating socket at pin 3! It was intermitent high resistence but brought all the voltages more in line.
It is goofy how messing with all this stuff has made it sound better and better. I should have made it clear that I am using all old stuff so that other hifi amp homebrewers can remember to check all the wild little wacky things that add up to the whole picture when debugging.
I replaced them to no avail, I touched up all solder joints etc. I am still redplating very slightly on the one tube socket but noticed that swapping the 2 tubes one is less red now. It is very slight in both tubes at the V4 EL84 socket with lights out. I think I am right at the threshold of the old RCA's and will put a 10 watt resistor in series at the 130 cathode bias resistor and knock it down just a tad. I have dropped voltages ever so slightly?? I did have a dirty tube socket on the non-redplating socket at pin 3! It was intermitent high resistence but brought all the voltages more in line.
It is goofy how messing with all this stuff has made it sound better and better. I should have made it clear that I am using all old stuff so that other hifi amp homebrewers can remember to check all the wild little wacky things that add up to the whole picture when debugging.
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zaphod_phil
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If you're using old stuff, like carbon comp resistors, be sure to check all your resistor values with a good DMM. It could be some bad resistors that are causing the red-palting problem.Wrongdog wrote: I should have made it clear that I am using all old stuff so that other hifi amp homebrewers can remember to check all the wild little wacky things that add up to the whole picture when debugging.
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Wrongdog
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All the resistors are new carbon comps from mouser and are typically sloppy at or near the 5% tolerences. I don't know why but I am a fool for the CC's. I guess if you are lucky the slop factor can also make the mojo magic.
BTW I am not usually lucky...
To clarify, the PT, OT, 40/30/10 can cap and tube and tube sockets and heater wiring are all 40+ years old. Pots, reisitors, orange drops etc are new.
WHat do you think about me changing the 130R to a 150 to see if it backs it down? Like I said i don't want to take down an EL84 but I do want to smack them hard. What else changes with that change?
BTW I am not usually lucky...
To clarify, the PT, OT, 40/30/10 can cap and tube and tube sockets and heater wiring are all 40+ years old. Pots, reisitors, orange drops etc are new.
WHat do you think about me changing the 130R to a 150 to see if it backs it down? Like I said i don't want to take down an EL84 but I do want to smack them hard. What else changes with that change?
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tedm
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a couple of comments
You may want to check out this thread:
http://www.18watt.com/modules.php?name= ... opic&t=103
basically, yes, you might have some success reducing redplating by increasing the cathode resistor to 150/180/220R from 125 or 130R, but note that my amp is slightly modded from an 18watt exact clone, so your measurements may vary.
Plate VDC may go up, but total dissipation may decrease.
Also, on the pro jr. may want to search the archives, someone here i think made an 18watt using the pro jr iron, and chassis, but I don't remember if they actually used the Pro Jr board or components.
http://www.18watt.com/modules.php?name= ... opic&t=103
basically, yes, you might have some success reducing redplating by increasing the cathode resistor to 150/180/220R from 125 or 130R, but note that my amp is slightly modded from an 18watt exact clone, so your measurements may vary.
Plate VDC may go up, but total dissipation may decrease.
Also, on the pro jr. may want to search the archives, someone here i think made an 18watt using the pro jr iron, and chassis, but I don't remember if they actually used the Pro Jr board or components.
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