Sound City 50 R

[OldSchoolDave]

The amp is clean and I noticed that it has two power tubes with the inscription XF3 B404 on the side of them,
are those Mullards ?
Also one Westinghouse 12AZ7A, what are these ?

From: http://www.gearslutz.com/board/geekslut ... tubes.html :

The filament/cathode ratings differ:

12AT7 (150mA & cathode 50V max)
12AZ7 (225 mA & cathode 250V max)

I've not seen a AZ7 used in guitar amps. Try a 12AT7/ECC81 in that socket.

Reverb circuits can induce all sorts of strange sounds. If there's any noise in front of the circuit, it can be exaggerated. Also, physically inspect the reverb tank, as the fine wires often get broken by rough handling of the amp.

The XF3's are Mullards. Enjoy !

Dave

[louis]

Thank's for the input Dave !

Below the other post ,D Yankee says,

I'm 100% positive the 12AT7 has more gain than the 12AU7; but you're correct than the 12AT7 has less gain than the 12AX7...

Infact, the 12AZ7 only has a mu of 60...so the alphabetical nomenclature (T - Z) doesn't necessarily mean higher mu (gain).



Louis

[OldSchoolDave]

Here's a handy chart I copied from some website somewhere (would credit the author, if I knew their name):

Preamp_Tube_GainFactors.jpg (43.01 KiB) Viewed 2312 times

Dave

[louis]

Thank's Dave !!

This is very helpfull for everyone .



Louis

[Zells]

Is there a quantifiable difference in gain factor between long plate and short plate ECC83/12AX7 tubes? It seems that long plate types generally have more gain in my experience.

[mhuss]

Maybe a tiny bit. A tube has to fit within certain specs (including gain) to qualify as a "12AX7" and we know the different tubes sound different, but it's not like a 12AX7 vs. a 12AT7 or anything.

---mark

[OldSchoolDave]

It seems that long plate types generally have more gain in my experience.

Probably more a factor of who made the particular long plate and during what era. Like Mark said, they're all supposed to meet a spec.

I've heard that long plates can also be more susceptible to being microphonic. Haven't run through enough comparisons to verify that. Has anyone here?

Dave

[Dr.HI-TONE]

yes in combos. The longer the plate, the more mass and leverage against the plates. More likely to vibrate.

[louis]

Modding a Sound City R into a JP model ?

Can it work and is it costy ...money and time wise ?

Thank's..............Louis

[mhuss]

This wouldn't be much harder than a normal SC to Hiwatt conversion, but you would need to find space for a couple of extra can caps.

--mark

[Dr.HI-TONE]

I think a SC100 or SC120 would be easier

[louis]

Thank's for the advise !

I'm asking cause I could get one for cheap .


Louis

[louis]

How many hours about would a pro tech take to mod the 50R into a JP

and how much parts would it take approx costwise ,,?



Thank's!.........Louis

[mhuss]

The parts wouldn't be much, maybe 50 USD. The hours -- that depends on the tech!

--mark

[Dr.HI-TONE]

Where would you put all the electrolytics in a SC50R? That chassis is a cramped clusterflock already. I would look for a SC120..IMHO