tame hi end on supro 24

[ALBATROS1234]

yesterday i finished a supro 24 clone. maybe call it a 24 lite because i omitted the tremolo. it fired right up and sounds damn good. i used the schematic on sluckeys sight and other than omitting the tremolo i gave it 1 input going to both control grids on v1 because i figured i would want the channels bridged anyway. so i want to shave a bit of high end off. my first instinct is to increase the input resistor size. originally the value of the "low" input had a 100k and "high" just had an .05 cap. i split the difference with a 47k since i just have 1 input. but there are also no grid stoppers on the 6973 tubes. should i try to pad them a bit? with a les paul i have to back tone off to 1 oclock and with my tele deluxe i have to back it off to 9 oclock. so i think it might be best if i shave off some highs. the question is what value should i start with? i dont want to dig down into that tight chassis multiple times to get to the pt sockets. my first guess is 33k -100k but i read some people use up to 200k on el84s sometimes. any advice?

[sluckey]

I just put a 470K on the input jack and ran a wire to a 2200 grid stopper at the tube socket. Since you want the channels permanently jumped just connect pin 2 and 7 together on the socket. So, 470K on the jack, one 2200 at the socket.

Next eliminate the extra 270K and .005 coupling cap just before one volume pot. IOW, make both channels look the same. Then change out both .005 couplers for .02 and replace both .01s on the power tube grids with .047s. Add a couple 1.5K or 5.6K grid stoppers. This should darken it a bit. However, I never considered this to be a bright amp.

[ALBATROS1234]

thanks man. i actually did omit the extra .005 and 270k on the tremolo channel because it didnt make sense and i think i actually posted that question when i was in the planning stages several months back.i actally built this thing but coundnt get the p.i. to work right so i shelved it. got plenty time atm. i also thought coupling caps might be a good move. perhaps the speaker is partly responsible i am using a 1950s alnico magnavox that is supposed to be close to a jenson. the speaker sounds great with my other amps but it is brighter than average. its brighter than any of my amps and with a les paul type usually most of my builds have the tone maxed or just slightly backed off, this amp i need to put it around 12 to 1 oclock to sound right and its my bassiest guitar so i am thinking i need to shave it a bit thanks sir.

[ALBATROS1234]

i may do it in increments like put the 470k and change the 1st set of coupling caps and see how it sounds etc. in general i really love the tone i guess thats why i thought of just padding the input and grid stoppers. thanks again for your reply.

[sluckey]

i actually did omit the extra .005 and 270k on the tremolo channel because it didnt make sense and i think i actually posted that question when i was in the planning stages several months back.

Remember the answer?

      http://el34world.com/Forum/index.php?topic=24744.msg267392#msg267392

[ALBATROS1234]

yea it was to boost highs for the trem channel so i omitted them. i actually started this amp back then but never quite got it finished. a few months back i broke down the parts that were giving me problems . its been sitting there until last week when i gutted it and re mounted the iron etc on a different chassis. then did a complete rebuild and this this for whatever reason it fired up. i was having p.i. problems. extremely low output. when i alligator clipped on to the p.i. of another build my power amp section worked fine. my v1 was fine . i could not understand why but the p.i. was killing the signal. so i tore it apart and re did it. works perfect now.

[tubeswell]

Probably a bad/dry/cold/something solder joint


FWIW, it's invariably always 'better' to go for full bandwidth in the input stage in order to minimise the proportion of noise floor in the overall amp signal (because whatever is in V1 gets amplified by every other stage), and then manipulate the bandpass/HF/LF signal from V2 onward.

[ALBATROS1234]

maybe so, i had it in my head the signal was somehow being pulled to ground but could not find fault with the wiring. i know i reflowed at least some of the connections. oh well doesnt matter anymore i made it better, stronger ,faster and it didnt cost 6 million bucks.