If you use one of the N-68X isolation transformers on the line cord input, then there is no need for any isolation on the guitar input, just connect the guitar ground to circuit ground and the guitar hot to the grid of the audio driver tube through a DC blocking cap of about 0.022 uF. The cap may not be required if the tube is cathode biased.
Okie doke. I'll see if I can locate a SAMS for the thing. I have really enjoyed SAMS over the years, but $22.00 per schematic is getting a bit pricey. If I was doing this kind of stuff for a living -- no problem 😀. Hopefully, a search will turn up something for free.
Here is the schematic of a guitar amp I made for about $50 using hot chassis radio tubes. The X2 terminals connect to the N-68X secondary, and X3 connect to the OPT, a $5 line matching transformer from Parts Express.
Awesome. Thanks for the great info, kind sir!
The input pentode stage is there for super overdriven (Jimi) sounds, and is not really needed. The phase inverter is a mosfet, but another tube could be used. This uses 100 mA series heater tubes from the last generation of tube radios before the transistor killed them all. 50C5's, 12AV6's, and 12AU6's could be used, or even 50L6's, 12SQ7's and 12SJ7's.
Hey, I have absolutely no problems with hybrid designs, and I've even thought about designing some kinda push-pull amp based on an IRF510 power MOSFET -- dirt cheap 😀 -- and a pair of 811's (have lots of em) in the final. I got to thinking about it, but I don't know if I have enough knowledge and expertise to properly design gear that uses inverters and such. I also don't think my knowledge is up to snuff enough to design a piece of gear that sounds decent by minimizing cross-over distortion as well. A man has to realize his limitations, and when that happens, it's time to read a book on the subject 😀. I guess there is a decent book out there on the subject?
I don't know. Maybe I'm underestimating myself or something. I know one thing for sure: I'm no TubeLab, Nelson Pass, or Robert Cordell -- that's for sure 😀.
These days, just wishful thinking. The only reason I'm able to interact at this level with you guys is that my Mom is in the hospital. I live 3 blocks away, so at least I can go visit often. When she comes home, it will be back to trying to help her. I can't do much for her with my health being bad, but at least I'm trying.
OTOH, I'm hoping that I can do these simple projects, like getting the AA5 going via Bluetooth. I was thinking about fixing another AA5 and using two of them as computer speakers and all-around listening to music 😀. Hell, I could even pipe my RF receivers through em, too 😀.
Plate to grid shorts are rare unless the tube has been physically abused.
Well, I was thinking along the lines of guitar players, and them lugging around their amplifiers. You know, without any doubts whatsoever, the physical abuse that they can do 😀. That, and they only bring in an amp when something REALLY goes wrong.
They are even rarer in small signal tubes....So maybe a 1 in a zillion short happens....you gave a cap in series with the input, so nothing other that the tube gets hurt. I have been abusing tubes in DIY guitar amps since the 1960's and I've never seen a plate to grid short in an input tube.
Yeah, I figured it would be low, and the DC-blocking cap would probably suffice 😀. OTOH, I try to visualize and picture situations happening in my head, and sometimes I over-analyze the situation, which is probably my major flaw 😀. I think a LOT of that has to do with designing gear for the oil biz. Everything has to be pretty much milspec to survive in harsh environments. I guess that way of thinking has crossed over to my rekindled hobby in audio 😀.
BTW, about over-clocking. What are your thoughts on the subject? I still can't bring myself to do it, even when I know this AMD PC box I purchased a month or two ago could easily take the abuse. I know it's become much more popular with RISC architectures. OTOH, I've read some stuff over the years about processor design, and they say that every processor produced is designed to meet maximum-design specifications, such as clock rate and such. Only after production tests show that a particular chip can't take a certain amount of heat and so on is when they are classified legit at a particular frequency.
Now, as far as overclocking the Teensy goes -- no problemo! 😀. (That would be "No Problemeaux" in French 😀 ). They are just a couple of bucks. I always balk and advise others to not even bother with it on $800.00 processors. OTOH, if that particular processor is getting long in the tooth, I tell them why not? They can do it, but I still can't bring myself to do it as well . LOL! The way I figure things is this: if the processor can't keep up and run the app smoothly, then it's time for something newer that can and doesn't require overclocking. I see it as processor abuse 😀. (Shrug.)
73,
Randy AB5NI
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Man, I already have the schematic. I forgot I found it awhile back. My memory is going with these damn meds. It looks like I can just jump in on the grid, Tube 😀.
73,
Randy AB5NI
73,
Randy AB5NI
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