TW input on pin 7 vs hiss

[Guus]

Hi Guy's,
like many builders and users of TW amps I had, from the start, some struggeling with the amound of hiss. With exeption of my SE Express that I've build, the Liverpool and Express had realy to much of it.
I've tried other tubes like 12AY7, ECC82, ECC81. It tempered the hiss but the sound changed in the wrong direction.

Then when looking at the schematic I was wondering, why did Ken F use pin 7 of V1 as an input? Normaly the input is pin 2. Why change that?
I realised Kenn once had a job at Ampeg and I also know that Ampeg used the 12DW7 tube in some type amplifiers. In that case the input is also on pin 7.
Eureka, could it be that Kenn first started with this type tube in V1? Or used it? It is imo an explaination to put the input on pin 7 of V1.
To see wath happens I put an ECC832 of JJ (same as 12DW7 or 7274) in V1 and switched the amp on. I heard nothing, was it on ?? Yes, it was on.
Result: no sign of any hiss, even at max amp volume. The amp is very quite, sensitive, transparant and you get that gradual sound from clean to distorion with volume pot of guitar. With a strat it doesn't break up at 9 o'clock that I had before. Best sound I got with amp volume at about 2-3 o'clock and working with guitar volume.
Even with the amp volume flat out I can dial in the desired guitar sound from clean to crunch and to all kind of different levels of distortion.

Maybe I am totaly wrong, but I was surprised how nice the amp sounded and how noise free it is with this kind of tube in V1.
Are there any TW users that followed this path ??

grtz
Guss

[M Fowler]

Some have said to use pin 6, 7, 8 triode as the first gain circuit least noise but I find that unsupported.

Ken positioned the tubes so pin 9 and 1 were on top next to the tone board so with that said, the first triode is 6, 7, 8. If he had a reason to do this, I would guess it was how he wanted the heater filament pins 4 & 5 positioned rather then making sure to use 6,7,8 triode first.

Mark

[rooster]

Hm. If I have it correctly, one side of this tube is a typical 12AX7, the other a 12AU7. Which is to say that plugged into the 12AU7 side you have a gain factor of 20 vs 100 on the !2AX7 side.

So, assuming you've used the 12AU7 side, this is not the same amp Ken designed. In this case, less hiss = less gain, not an option that says 'Express'.

[M Fowler]

Well there are two versions of tubes to try the ECC832 and the ECC823 they are opposite of each other.

[Guus]

Hi guy's,

thanks for the reply.
As said I'm trying to find somethng to fix the hiss problem.

Ofcourse gives the use of a ECC832 less gain.
But, with a ECC83 in the input stage there is imo no practicle use of a gain setting from 3/4 to max volume. (Explosion level)
With the use of a ECC832 it shifts the gainrange on the volume pot.
So you have to set the volume pot a little higher to get the same output and the desired distortion level.
Fact is that in my case I now can use the complete volume range from 0 to 10 and this with no anoying hiss.
Stays he question, does the sound change?
With testing I couldn't hear much difference, I could get the same sound, feel, etc.
Anyone who wants to try it and give a respons?

grtz
Guss

[rooster]

A few here, myself included, have changed to a 500K volume pot in the Express. Either way, 1M or 500K, I would never be turning that knob up to '10' but - IMO - the circuit syncs better with the 500K for my tastes. The hiss is nothing here, really. It exists in a certain band and it might be louder in your amp than mine, I dunno. My tubes are Holland Amperex I63 in V1, Mullard V2, back another Amperex in V3, and Mullard XF2s in V4 and V5 (biased at 28 mAs). I use the stock NOS Mallory OD caps.

Glen has mentioned a few times that he has a very slow ramp up on one of his volume pots, and says that 12 o'clock is actually barely cracking things. Eh, so there's something about the volume pot in these amps that needs to be considered maybe. Or not.

Believe me, when your Express is really dialed in the hiss will not be a problem - for either live play or recording. In fact, there's a super clean no frills recording here (this site) somewhere using one of my Express amps using the LarMar MV, turning the MV knob from 0 to 10. Listen to it maybe, and you'll understand better perhaps.

[M Fowler]

I tried the Northern 12AX7 tubes in my last Express head and it was within the tolerable hiss level

http://www.thetubestore.com/Tubes/Northern-Electric

[geetarpicker]

A few here, myself included, have changed to a 500K volume pot in the Express. Either way, 1M or 500K, I would never be turning that knob up to '10' but - IMO - the circuit syncs better with the 500K for my tastes. The hiss is nothing here, really. It exists in a certain band and it might be louder in your amp than mine, I dunno. My tubes are Holland Amperex I63 in V1, Mullard V2, back another Amperex in V3, and Mullard XF2s in V4 and V5 (biased at 28 mAs). I use the stock NOS Mallory OD caps.

Glen has mentioned a few times that he has a very slow ramp up on one of his volume pots, and says that 12 o'clock is actually barely cracking things. Eh, so there's something about the volume pot in these amps that needs to be considered maybe. Or not.

Believe me, when your Express is really dialed in the hiss will not be a problem - for either live play or recording. In fact, there's a super clean no frills recording here (this site) somewhere using one of my Express amps using the LarMar MV, turning the MV knob from 0 to 10. Listen to it maybe, and you'll understand better perhaps.

To clarify... on my '85 Express 1/4 way is barely playing, noon is definitely breaking up but still modest with a single coil guitar, 3/4 is gainy however from 3/4 to full up there is still a noticeable gain difference. One or two o'clock seems to be the sweet spot on this amp. That said the "1 meg" volume pot measures pretty high at about 1.3meg wide open, but only measures about 80k on 1/2.

[Guus]

Hi guys,

thanks for replys.
I must say, with the use of a ECC832 I get the same response on the Volume pot like Geetarpicker.
Until I find an other/better solution for the hiss, I go with the ECC832.

grtz
Guss