Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on March 11, 2020, 12:51:01 pm
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Does anyone have a schematic or layout of a speaker cab switch to go from 4 ohms to 16 ohms, using two 8 ohm speakers. Obliviously, the switch would put the speakers in parallel and series.
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Sorry, posted in wrong area but I just figured it out using a DPDT. (+, -) to center lugs, connect the two top lugs, and (-,+) to bottom lugs of switch. One side, 4 ohms in parallel other 16 ohms in series.
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This works...
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My way did't work but I can't understand your diagram.
There are six lugs on a DPDT switch, the bottom two lugs are connected the middle lugs go one side to +, one side to - to the speakers. But I'm lost from there. I don't see the top lugs or where they go to the jack, are they not used?
I see up is parallel bu tcan't see down as series. What am I missing
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Any better? Circle Plus is the jack tip. Circle Negative is the jack sleeve.
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Yes, thank you. I'll wire the two 8 ohm's cab tomorrow, this is driving me nuts but the last diagram looks doable for me. Hope the lugs on the switch hold up, soldered the piss out them, on and off, ha.
Same diagram as the first but I see the top two lugs, l assume the first diagram was just missing the dot's designating the connection. BTW, l blew up my meter firing up a 6v6 Plexi, couldn't figure out what was going on, had run away bias current, over 200mA's. I had put protection diodes on the 5ar4, maybe I put them on backwards, or the wrong diode, took them off, fired up. I used a different diode on the rectifier tube then a 1n007, maybe I had the band the wrong way. Band toward pin 6 and 4.
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mo better?
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Mo better, works perfectly, thank you. Found out it makes a big difference in the gauge of the wire using the diagram. 22 gauge wire was not accurate, ohms were high on 16 ohm side and jumping around, had a good speaker cable. Changed out the wire to 18 stranded, made good connections and much more accurate, 3.8 on the four side and 17.1 on the 16 side, two 8 ohm speakers.
Rather than open a new topic, I tried 6L6s in this 6V6 Plexi, exact match to yours, except I didn't have .68 caps, used 1uf, no hearable difference, I figure.
With the 6L6s I can't seem to get them biased more then 65% dissipation, as I turn up the current draw, mA's the plate voltage goes down too low, Weber's bias calculator, gives 70% dissipation at a set voltage, turning bias to that mA setting lowers the plate voltage below what is posted. I hope this makes sense.
Could it be the resistors to the bias are 100K and not 220K? Amp sounds decent with 6L6s but with volume up, a little ratty, maybe due to cold bias but not too bad, might just be me. If it's the the 100K, maybe I could compensate with say 150K?
Amp sounds great with 6V6s, but B+ seems high, 420v, all these Hammond AO-43 PT's I've use (330-0-330) give me that high B+ voltage, I see your specs are 400 range.
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you two have been holding hands long enough, time for a room :laugh:
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time for a room :laugh:
A room...? Not unless he's, 35-25-36 :icon_biggrin: