unclej Posted December 6, 2004 Report Share Posted December 6, 2004 the other day i mentioned that i had acquired an old alamo "paragon bass" amp head. i've been searching for a schematic with no luck. two of the tubes are missing so i don't know what to replace them with. i just googled "paragon bass amp tubes" and one of the results was a harmony central review for an alamo "paragon special". from the detailed description the fellow gave it appears to be the same amp that i have only in a cabinet with speaker/s. he detailed the voltage, the wattage, the switches, pots, inputs, outputs, etc. it's all exactly the same as mine. here's the question: he gave a list of all of the tubes. (2) 12ax7's, (1) 7199, (2) 5881's and (1) 5u4. all of these tubes are present in my amp except the two 5881's listed in the review. how safe would i be in assuming that these were the two that i needed? and if they're not right how much damage could they do. Quote Link to comment Share on other sites More sharing options...
Drak Posted December 6, 2004 Report Share Posted December 6, 2004 I'd say you were pretty safe in assuming you're on the right track. You can replace the 5881's with 6l6GB's or GC's. The GB is the closer match. You wouldn't burn it down as long as you stayed within the 6L6/5881/6V6 family. Quote Link to comment Share on other sites More sharing options...
JohnnyG Posted December 6, 2004 Report Share Posted December 6, 2004 as far as i know the worst you can do is have them biased too hot which could lead to the output tranny and/or the tubes frying. id try to work out what the biasing voltage would be if you had those tubes in and then check to see what the biasing would need to be Quote Link to comment Share on other sites More sharing options...
unclej Posted December 6, 2004 Author Report Share Posted December 6, 2004 thanks drak, johnnyg..i just found a pretty detailed history of the alamo co. and there were a couple of variations of the paragon bass and all of them listed the 5881 so i'm going to give them a try. Quote Link to comment Share on other sites More sharing options...
Drak Posted December 6, 2004 Report Share Posted December 6, 2004 Being the amps' that old, I would recommend going with a pair of NOS or UOS 5881's and not those new jobs they offer these days. The old 5881's are far more robust than what they make today. Even a pair of used Tung Sol's or RCA rebrands would be my pick over the new stuff until you get everything squared away on it, but that's just a recommendation, not a necessity. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted December 7, 2004 Report Share Posted December 7, 2004 (2) 12ax7's, (1) 7199, (2) 5881's and (1) 5u4 The only info I could find on a Paragon Bass amp shows the same tube line-up except the 7199 is replaced with a 6AN8 - since they're both triode/pentode combos in a 9-pin package (but with different pinouts), you'd have to trace the circuit to see which one your unit uses. 30 Watts really isn't pushing a pair of 5881s very hard, and 6L6s will handle even more current, so I wouldn't worry about the power section, but it's going to be imperative to sort out the pinout on that "mystery" tube. Here's the basic data and pinout for both tubes: 6AN8 7199 I'd grab that schematic! Even if it's not 100%, it'll give you a starting point, and it's gotta be pretty close! Quote Link to comment Share on other sites More sharing options...
Drak Posted December 7, 2004 Report Share Posted December 7, 2004 That tube selection is -awfully- close to Ampeg-land. I smell a connection to Ampeg somewhere along the chain. The middle period Ampeg Reverborockets/Jets/Rockets used -almost- that exact same lineup, including the 7199, once they switched over to the 9-pin mini tubes away from the old octals, which would place it around, ohhh, '64-65-ish? And the later Ampegs, the very late '60's and '70's models, some used that 6AN8. I've owned several old early '60's Reverborockets and Rockets, and a later mid-70's VT22, affectionately known as -The Howitzer-. That thing would bury any Marshall or Fender Twin out there. If you could actually pick it up and carry it anywhere, hehehe. Quote Link to comment Share on other sites More sharing options...
unclej Posted December 7, 2004 Author Report Share Posted December 7, 2004 thanks lk, drak...i'd be really happy if i was able to find a schematic on it but so far i haven't had any luck. if these dang customers would quit bothering me i'd have more time to do the important stuff. drak, i read what seems to be a pretty comprehensive history of the alamo company and they didn't mention any connection to ampeg..i guess that doesn't mean that they couldn't have "borrowed" some ideas though. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted December 7, 2004 Report Share Posted December 7, 2004 It's more likely that they had the same tube book - almost all of the amps from the 40s and 50s were lifted pretty much verbatim from either the GE, Western Electric, or RCA tube manuals (and that includes Leo and Doc's masterpieces). Call it "parallel evolution". Unc, did you ever get in touch with the Just Radio people to see what they had? Quote Link to comment Share on other sites More sharing options...
unclej Posted December 8, 2004 Author Report Share Posted December 8, 2004 yes i did lk and they were helpful but didn't have it. they gave me a couple of suggestions where to look and no luck there either. it's out there somewhere in cyberworld so i'll find it eventually. since it's mine and not a customer's there's no real rush. by the way, i like the "parallel evolution" theory...i just might have to borrow that sometime. Quote Link to comment Share on other sites More sharing options...
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