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Hello Mark, Oh, I forgot about that, right. So even if they are separated by a resistor this rule still stands? Thank you for highlighting that for me! Fred

Hi all, I came back to this thread to ask a question, but started by just re-reading the whole thing as I think I know a bit more now than I did back then, I'd like to say thanks again to everyone who helped me build up a bit more knowledge, little by little. An Happy New Year everyone too! So...

I’ve been taking apart a few old tube stereo consoles to convert them to guitar amp. Some old solid state stereos I took apart for parts too, so I can mod the tube ones. First one was a Sparton brand, with two single ended power amp channels (they are stereo, duh!) I kept one and built a JCM800...

Mine is an SP-3 and it is a 03/78. Maybe the use of the different boards depends on the options and not only the dates? I don’t have a reverb, and I saw some of the mark 1 preamp boards had an additional preamp tube compared to mine, I guess it was the reberb tube. Fred

Can see it a bit here, moslty hidden under all the wiring on the tube socket. From this angle it almost looks like the red wire is jumped with the point where the resistor ends. But that’s not how I saw it when I traced it... maybe a mistake, I might have a look tonight to confirm. Anything...

Hey Mark, the resistor is on the circuit board. I am on the phone now but will look at the pictures to try and find it when I’m on the computer a bit later. Glad the pictures and schematic notes of my Mark 1 can be useful for you guys! Fred

Hi there, Here is a picture where you see how it is wrapped, it’s the red wire around the three gray coax. I’ll see which other pictures show it from other angles. By the way here is the thread with all pictures (now that you see the wire it might be easier to spot in in the other pics...

Hello Mark, Here are the voltages at the documented points in the schematics. I have not taken the time yet to compare with your values though, you can see my measured voltages in blue.

I wondered that too about the 5 preamp tubes, maybe the EQ requires an additional tube? In mine there are 4 and it’s because of the fx loop. No reverb or eq.

Hey Jim, congrats on the nice score :) feel free to put some pics! What speakers does it have? Is it still running the fetron in V1 position? The options were available and you had to choose whatever you wanted and it was built to order. 60 or 100w, reverb, GEQ for instance were all options...

Hi Mark, Next time I have some bench time with mine I will measure, if you have not received answers by then. Frederik

No problem, you are welcome. I read somewhere when there are only two digits before a K it means the value is exactly in pF. But caps markings “conventions” are quite eclectic, if not cahotic lol

Hello Mark, I'm glad I could help you a bit with it. I looked again and the value is actually 47K, so if I understand correctly, 47K being 47pF it would be 0.047nF and not uF! Sorry about the mistake, I will update the schematic, below is a picture of the cap with the writing on it. Fred

Hello Mark, Regarding the FX loop, I have no intention of getting rid of it, I was mostly doing some archeology :D I was interested to know more about the story of my amp. Regarding the cap, sorry for the delay, the devices I was on did not have the password memorized and I could not get back...

Hey there all, Recently I have been documenting my Boogie Mark 1 so I can convert it to use 12AX7 optimally, instead of the current "ok for 12AX7 but really made for Fetron" circuit, I made a thread here about that, I am learning a lot with all you guys helping...

The more I read about NFB, the more I think yes I do like my amp as it currently is, but I also feel like there would be some interesting tones to try with a reduced NFB. If it ends up being a very reversible mod, maybe at some point I will give it a try, but I'm not ready for that yet. I have...

Thanks twintriode for the information! I did play with using all 12AX7 many years ago (instead of the 12AT7) but I did not feel like the difference was big. I could try that again though since I put more time on understanding the amp through the years. I will try the EQ before the amp to see...

Thank you CrustyBooger for your input. I certainly don't want to fiddle with things and end up with a bad sounding amp, yes I want to understand why it sounds like it does, and if some reversible minor modifications can be done to explore new sounds, who knows, maybe I'll do some tests in the...

I am still learning so I really am unsure, but what I understand from the article below is the two resistor determines the feedback voltage, which appears to be the important factor given how the tube acts as a voltage amplifier. But it also says that the transformer tap is important in the...

Thank you "CrustyBugger" for the precious history details and your input on my amp! Helps me understand it more and why it is that way, and how different it potentially is from other variations of the Mark 1. I really like the presence control as it is so I do not think I am going to play with...