Metropoulos Forum

oh i have such cap, i might give it a try, thanks.
Although i didn't see what you meant about unhooking the bass pot . ? unsoldering it ?

is it a volume mod or a gain mod actualy ?

i was thinking of what makes van halen's amp to sound this way, other than the variac. i could have fun doing it.

really, the controls have really not much effect, quite weak, it's surprising, when i compare it to the 45/100.

do i remember well that jimi had his amps without the volume cap ?

WHen you get it right, try it again anmd perhaps with 6550 or KT88 output tubes...see if you can get closer to BOG sound this time.

I just put KT88s in my 69 build. I was going to try 6550s, but I was convinced by Tube Tramp to try KT88s instead as he likes them much better, but they should be very similar. Initital impressions were great - like a broadband, high-def version of the same amp, and dare I say it...pretty close to BOG.

Hi Thorleif !

well, this was the first thing i wanted to try, after these corrections, since indeed my comparison with the 45/100 was biased because of some big newbie mistakes, since i build this amp with mistakes back then.
But, for a SL with el34, the 45/100 still wins for me. it does a very good hendrix and machine gun tone anyway, but more about some other concerts. still hi fi, and missing some crucial thing hard to describe.

so you say that i can directly put some kt88 into this superlead ? and play it directly ?
aren't kt88 close to the kt66 of the 45/100 ?

what's a broadband ?

kt88s require rebiasing and lowered bias resistors. many also prefer to reduce NFB.

6550s are not optimal in 100w plexis, partially because the screen voltage exceed the allowed 440v with ca 10%. kt88s are much better in this respect

Thanks.

Well , if someday i have money , i could try.

Yes, bias splitter resistors should be lowered from 220k to 100k. And you will need more negative bias voltage available to get then bases in the right range. You can either lover the 27k before the diode in the bias circuit, or increase the resistor going to the bias pot (May not be enough by itself?). I just did some very brief tests with alligator clips and ballpark bias, but it's got more clarity, especially in the bass, which is exactly what's missing from EL34s. May also account for why you like a KT66 amp better for BOG tones...the KT66 and KT88 are both kinkless tetrodes...don't ask me to explain, but they are basically more linear and "hi-fi" than any EL34, certainly in this type of application. BOG tone is all about clarity...

Thanks for the tip.

Glad to you guys back !

My previous sertings had my superlead with a lot of clarity. And more trebles.
Now that it's corrected, it lost some i feel.

To me the bog tone isn't hi fi at all, but yes it's played with a clean settings on the amp.
There's something more, in the bog tone, hard to describe, other than clarity.
Or i end up with some ils of whight clarity or berkeley.

if you half the bias splitter resistors you also need to double the coupling caps to get the same bass response from the PI/driver.

.022uf & 220k equals .0484uf and 100k

hey cool !

Thanks Roe !