Wow my amp sounds amazing now!!!

[Danhalen]

I just reread my post about "aggressive but not shrill" and realized that it didn't make much sense. Oh well. It was late when I wrote that. Regardless I tried a bunch of stuff and found a spec that is pretty close to perfect for my taste (at least for now )

Basically it's a 1986 with a .68 on V2a and lower filtering. Ok so maybe its like a JTM 50 with a .68 on V2a. Here's what I've got:

Standard shared cathode setup
.68 on V2a
56/250 tonestack
.1uf's in the phase inverter
Negative feedback is 27k
No bright cap
Filtering is:
Mains 50uf
PI 32uf
Screens 32uf
Preamp dual 32uf

Ever since I got the amp I have been struggling with the stiffness of the amp. Lowering the negative feedback loosened it up but not in the way I wanted. Until today I had only tried 47k or 100k. 27k really did it for me. It gives a really nice woodiness to the sound. The lower filtering on the mains and screens/PI give just a bit of sag to the sound but the 27k kind of keeps it in check. The .68 (no piggyback resistor) just gives the amp a bit of focus/aggression just enough for my taste. This is exactly the sound/feel I had in my head. The only thing I want to tweak now is the capacitor value for the first cathode to tame a little bit of flubbiness which is actually not too bad. Also, with the lower filtering there is no ghosting whatsoever.

My SG, SG jr and my friend's Tokai strat all sound exactly as they should to my ears. The neck pickup of the strat gives the best Hendrix sound I've ever had under my fingers. The 27k is a BIG part of the sound IMO.

I'm going to use the amp as is for rehearsal today. I think my bandmates are going to be impressed!

I highly recommend this setup!

[chrisom]

We need to hear a short MP3 of it with: a little Zeppelin, a little Free, a little AC/DC, and a little VH to make a proper judgement... I bet it rocks..!

[Danhalen]

I agree. I'll try and get something together today!

[VelvetGeorge]

Are you saying you have no cathode resistor on V2a? Only the .68uf cap?

Sorry if I misread.

george

[Danhalen]

Hi George,

Yup no resistor, just the .68 cap. Is that bad?

P.S. I'm going to try and post a clip today with the SG Jr and the strat. My "regular" SG is being reworked currently. I was playing it again last night and man the amps sounds just amazing. The tiny bit of "flubby" bass actually sounds awesome, gives it a nice fuzzy kind of quality when the guitar is cranked, but when backed off a bit it tightens up a bit as it cleans up. I may still experiment with trying to tighten the bass response it a little, just the slightest bit. Although I must say I'm pretty pleased as is!

P.P.S. I forgot to mention in my original post that the negative feedback is tied to the speaker jack. So it is 27k to the speaker jack.

[PCollen]

You state you have a .68uF cap on V2a (I assume it's a cathode bias cap, Ck), and later you say: "The .68 (no piggyback resistor) ...."

What do you mean by 'no piggyback resistor' ? Good Lord....you don't mean....no...SERIOUSLY ?

[PCollen]

Hi George,

Yup no resistor, just the .68 cap. Is that bad?

.

So you just have a capacitor between V2a cathode (pin 3) and ground , no cathode resistor ? Amazing.....

[Danhalen]

I'm not sure what I meant when I wrote no piggyback resistor. There is the usual 820ohm resistor in that spot.

However, at one point I had inadvertantly sent one of the V1 cathodes straight to ground. I thought I was making the amp shared cathode when in reality it was split cathode with the bright channel cathode going straight to ground! The amp actually sounded really great like that!

I am very interested as to what the negative effect of this would be (no cathode bias resistor)? Or to put it another way, I would like to learn more about what a cathode resistor does. I understand that it sets the bias of the tube, but what would happen if it was not there? Anyone have any info?

Also, why would have the V1b cathode sounded so good straight to ground?

[jonamojo]

Hmmm I'm sure no one was trying to be condescending to you, just trying to understand how your amp was still functioning, I'm sure someone with more knowledge will chime in.

[Danhalen]

Well now the amp is a lot closer to JTM specs. I took the .68 off of V2 and put on a 250pf bright cap. With no bright cap and no V2 bypass the amp sounded a little too "open". The .68 on V2 added a bit of high mid cut which I liked better than nothing. But with no V2 bypass and the 250pf bright cap there is a nice little bit of sparkle which is more interesting. It sounds awesome.

I also went from 330uf/820 on the v1 cathode to 220uf/820. I noticed a slight difference there too. Something in the low harmonics is a little less woofy/wonky, although the tone is basically the same. Just a little more clarity maybe. I will try and post some clips asap. It really sounds great!

Also, still wondering. Is it safe to send either of the v1 or v2 cathodes straight to ground?

[itsonlyadam]

So referring back to the specs you posted originally (.68uF V2a bypass cap, et. al.), what would you say the sound was like? I'm considering a '68 1986 Bass 50W to similar specs (pretty much the same but including a 1000pF bright cap and a 47K NFB resistor to the 16 ohm tap), and would figure your original setup (at the time of the first post) would sound very similar to my proposed specs. So I wanted some feedback before I pull the trigger. Was it badass? Did it scream Paul Kossoff? Jimmy Page? Duane Allman? I guess what I want to know is how dirty was it? I play a Les Paul and heard the sound may be a little muddy, but I figured with the V2a bypass cap I would get a noticeable mid- to high-range boost. So let me know what comparable sounds (if any) might your amp yield.

[Danhalen]

Hi Adam,

I would say the bass circuit with the .68 on V2a reminded me a lot of the sound Paul Kossoff had on the Free Live album. "I'm a Mover" from that record that is pretty much what it sounded like nearly cranked. I would say it could get muddy if you wanted to play chords with the amp and your guitar cranked. However the clean or on the edge of breakup sound is very clear (but not as sparkly as it is now with no V2 bypass cap and a bright cap on volume II).

For me it's almost perfect now, because I usually use a cleaner sound for rhythm playing (guitar volume rolled back a bit) and like the fuzzy fat sound I get when cranking the guitar volume for leads or dirty fuzzy power chords (often with the tone control rolled back a little). Remember the sound I am getting now is very similar, just a tad more open and chimey on cleaner sounds. The .68 is not a drastic difference. The cleaner sound is definitely better without the .68. The dirty sound is a matter of taste with or without. Hope that makes sense!

[razelfrax]

Hey Dan what have you got your impedance selector set at and what kind of cabinet are you using ?

[Danhalen]

The amp is set to 16ohms through a Metropoulos 4x12 (an earlier one) with Celestion Heritage Greenbacks. I currently have the negative feedback connected to the speaker jack but I will be moving it to the 8ohm tap since i like the slightly looser feel of the 8ohm setting now.

[Danhalen]

Well I did something stupid the other day but it sort of has a happy ending... I blew my output transformer! I played through my amp with no cab attached. I blame being very tired but it still was pretty dumb. Anyhow long story short, my local amp tech sold me an early 70's jmp OT which is now in my amp. I also completely retubed it with Tungsol reissues in the preamp and Electro Harmonix EL34's. With the new OT and new tubes the amp sounds even better than ever!

This is how I've got it now (and probably how it will stay for a while):

220uf on V1 cathode
Bass tonestack
100pf bright cap
.022's in the pi
27k negative feedback connected to the 8ohm tap
50uf Mains filtering
32uf filtering for pi, screens and preamp

Tonight at practice I used my Les Paul Jr and my Rickenbacker 12 for fun which sounded awesome.