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Posted: Thu Nov 25, 2010 6:15 am
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OP: Sorry for hijacking your thread. Embarassed

that was my EVIL plan all along muhaha :twisted:

i also tried lower gain tubes.
it also sounded too sterile and cut the gain from the overdrive.
i tried some TADs philips NOS(which was awful!!!) and sovteks.
as i see if want less gain just stick your guitar to jack 2 to me it sounded the same as putting the low gain tubes :roll:
the major impact on the sound was biasing the GT 6L6CHP to 74 mv!
ofcourse i got greedy and biased it higher :lol: but then the sound started to be thinner and compressed.
i tell ya, that 74 mv is the magic spot for the GT's 6L6CHP!

i use the overdrive channel only for late night blues jamming.
when i want to go heavy i use twin tube classic with the clean channel.
man the HRD clean with the MOD and this pedal could make even a metal head pleased
8)
sounds mesa boogish distortion like.


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Posted: Thu Nov 25, 2010 6:49 am
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Yes, back to the OP.

The cap change on the master is raising the cutoff frequency of the bypass. You're not really adding highs, just getting rid of a little high mids. Different caps will sound different. (ie: ceramic, silver mica, etc.)

The cap add is a great way of testing caps, however, I wouldn't leave it this way. This cap parallel thing is one of the reasons CBS was frowned upon when they took over Fender in the 60's. A .0022uf or around there would work, and increasing the value increases bass.

Just my opinion though, whatever sounds right to you is the important thing.


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Posted: Thu Nov 25, 2010 7:24 am
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You're not really adding highs

yes you are right.
many of the people out there modding want to cut the highs more.
i'm on the other side prefer they will be there and cut them the way i want.
i think the stock speaker really doesn't handle highs above 4Khz good.
with the celestion vintage 30 actually letting more high frequency pass makes the sound more alive and SRV like.

Quote:
This cap parallel thing is one of the reasons CBS was frowned upon when they took over Fender in the 60's

please do tell more :D


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Posted: Thu Nov 25, 2010 7:53 am
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I like the vintage 30 speaker, but to me it sounds like it belongs in a British type EL34 amp with cranking overdrive. I buy Fender amps because they sound like a Fender amp. If a want an overdrive beast, I'll get a Marshall with Celestions. My tastes have changed through the years, and as I get older, I prefer the Fender tone. Eric Johnson uses Fender for clean and gritty and Marshall for lead. I use a pedal for convenience.

On the parallel cap thing, techs were opening up amps during the early CBS era and finding parallel coupling caps sometimes, probably because CBS Fender ran out of a particular value. Using their basic electronic knowledge, they subbed. IMHO, parallel caps are great if you are running an electric motor, but not so good if you are amplifying a guitar signal. You are asking 2 different components to pass the same signal at the same time with the same tone. Seems questionable to me, since it's all about tone. I'm more comfortable asking 1 cap to do it.


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Posted: Thu Nov 25, 2010 8:00 am
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babatube wrote:
Quote:
OP: Sorry for hijacking your thread. Embarassed

that was my EVIL plan all along muhaha :twisted:

i also tried lower gain tubes.
it also sounded too sterile and cut the gain from the overdrive.
i tried some TADs philips NOS(which was awful!!!) and sovteks.
as i see if want less gain just stick your guitar to jack 2 to me it sounded the same as putting the low gain tubes :roll:
the major impact on the sound was biasing the GT 6L6CHP to 74 mv!
ofcourse i got greedy and biased it higher :lol: but then the sound started to be thinner and compressed.
i tell ya, that 74 mv is the magic spot for the GT's 6L6CHP!

i use the overdrive channel only for late night blues jamming.
when i want to go heavy i use twin tube classic with the clean channel.
man the HRD clean with the MOD and this pedal could make even a metal head pleased
8)
sounds mesa boogish distortion like.


I too play through input #2 with my BDRI. I don't play professionally, just at home in my studio.

With the stock GT 6L6Rs (which are really Sovtek 5881WXTs) in the BDRI, I too found that it sounded best when biased around 70 - 75 mV. I settled on 70 mV as best for those tubes. I am now running this JJ tubeset from Eurotubes:

Fender Blues Deluxe-Deville Blues Option
Price: $66.25
Description: A hotter matched pair of the JJ 6L6GC's for the reissue or the original fixed bias 90's Blues Deluxe or Deville for a big warm tone along with a standard ECC83S for V1, an ECC81 for V2 to drop the gain with one balanced ECC83S for the phase inverter in V3. These will reduce the preamp gain for players wanting less gain.


I have the 6L6GCs biased at 85 mV (which is about 38.5 mA cathode current/37 mA plate current at 414 VDC plate voltage as measured by my bias probe and the Weber bias tables). The BDRI sounds really sweet with a great blues tone. I don't use the OD channel (there really isn't much OD, especially with the ECC81 in V2), instead using a Monte Allums Supra Plus modded Boss OD-3. Great tone. The stock speaker even sounds good with this setup. :D

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Posted: Thu Nov 25, 2010 8:05 am
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rjake wrote:
On the parallel cap thing, techs were opening up amps during the early CBS era and finding parallel coupling caps sometimes, probably because CBS Fender ran out of a particular value. Using their basic electronic knowledge, they subbed. IMHO, parallel caps are great if you are running an electric motor, but not so good if you are amplifying a guitar signal. You are asking 2 different components to pass the same signal at the same time with the same tone. Seems questionable to me, since it's all about tone. I'm more comfortable asking 1 cap to do it.


I can imagine that there might be a slight phase shift in the signal running through two parallel mounted caps as the complex impedance for each one individually would be different. How much of a phase shift would be required to make a noticable difference in tone I don't know.

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Posted: Thu Nov 25, 2010 8:31 am
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I have the 6L6GCs biased at 85 mV

:shock: :shock: :shock:
wow that's hot! in a tubish way ofcourse :lol:
are these the GT's 6L6 or other brand?

Quote:
since it's all about tone. I'm more comfortable asking 1 cap to do it.


i'm ok with the slight phase shifts.i'm sure 1 cap will sound better but i couldn't bother taking apart the PCB.


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Posted: Thu Nov 25, 2010 8:42 am
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Quote:
I can imagine that there might be a slight phase shift in the signal running through two parallel mounted caps as the complex impedance for each one individually would be different. How much of a phase shift would be required to make a noticable difference in tone I don't know.


That's enough for me to "just say no".


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Posted: Thu Nov 25, 2010 9:14 am
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One of the easier mods is the r103 clip reverb mod .
Described here http://www.justinholton.com/hotrod/reverb.html

Works on the HRD's and the BD's. small change to the reverb circuit function / sound.

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Posted: Thu Nov 25, 2010 10:22 am
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babatube wrote:
Quote:
I have the 6L6GCs biased at 85 mV


:shock: :shock: :shock:
wow that's hot! in a tubish way ofcourse :lol:
are these the GT's 6L6 or other brand?


You didn't read my post close enough or don't understand tube biasing.

The tubes are JJs from Eurotubes.

75 or 85 mV by itself is meaningless. You need to know plate current and plate voltage and calculate the tube dissipation.

37 mA plate current X 414 VDC plate voltage is 15.1 watts. That's only 50% of the rated tube power and quite safe. Not hot at all. 8)

Do a search. There have been a lot of discussions between myself, shimmilou, and others on power tube biasing. :D

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Posted: Thu Nov 25, 2010 11:24 am
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37 mA plate current X 414 VDC plate voltage is 15.1 watts. That's only 50% of the rated tube power and quite safe. Not hot at all.


Another thing to remember is, 50% rated power at idle. Throw some guitar licks in there and the current and voltage will very a bit. You may see 70% or around 20 watts peak, well within the rated limits of a 6L6GC.


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Posted: Thu Nov 25, 2010 11:33 am
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rjake wrote:
Quote:
37 mA plate current X 414 VDC plate voltage is 15.1 watts. That's only 50% of the rated tube power and quite safe. Not hot at all.


Another thing to remember is, 50% rated power at idle. Throw some guitar licks in there and the current and voltage will very a bit. You may see 70% or around 20 watts peak, well within the rated limits of a 6L6GC.


Yes, bias is measured at idle. I thought that was self explanatory, but maybe not.

70% at idle is safe also, although it may shorten tube life some. To tell the truth, from what I have measured on my BDRI, and given the power supply in the BDRI and HRD, I'm not sure you can ever reach 70% plate dissipation at idle with anything in the Hot Rod series. Maybe the HR/BD Deville as that has a more potent power supply,

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Posted: Thu Nov 25, 2010 11:56 am
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Just didn't want anybody biasing at 95% thinking it was safe. Some folks on here are not electronics techs or tube gurus like yourself.


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Posted: Thu Nov 25, 2010 1:44 pm
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You didn't read my post close enough or don't understand tube biasing.

you got me
but i know ear biasing :lol:

i never claimed to be an electronic guru.
i used suggestions from other people who experimented and let my ears decide.

this a simple mod where anyone who can handle a Soldering iron can do.
if i knew more and had your knowledge i would build myself an amp :twisted:
probably a JCM 800 preamp with an HRD power amp combination.
one can only dream...


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Posted: Thu Nov 25, 2010 7:44 pm
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rjake wrote:
Just didn't want anybody biasing at 95% thinking it was safe. Some folks on here are not electronics techs or tube gurus like yourself.


Hardly a tube guru. I have a BSEE (1976), but most of what I learned about guitar amps I learned from the many more knowledgable people in this forum.

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