I am in need of new tubes.

Kerouac

Kerouac

weird musical dildo
For my VHT Pitbull 45 comco. According to the spec sheet:

TUBE FUNCTION AND LOCATION CHART PITTBULL FORTY-FIVE 1X12 COMBO Early Version

Each 12AX7 has two sections/functions. Section A is shown first, Section B is second. Factory recommended tubes are listed under each location. Numbering sequence is right

page1image2824
page1image2984

to left looking at back

V1 (shielded tube) 12AX7WB Russia

V2
12AX7 China

V3
12AX7 China

V4 EL84

V5
12AX7 China

V6
5AR4 Russia

of amp starting with the row closest to front panel of amp.

Gain Stage 2 for Drive channel*
Input Gain Stage 1 and signal splitter for both channels

Tone Control Driver, Drive channel Gain Stage 3 for Drive channel

Gain Stage 2 for Clean channel Reverb return amplifier*

Reverb Driver. Small Signal Pentode
Not interchangeable with 12AX7 or EF86

Phase Inverter
Power amp input stage

Rectifier Tube

Power Tubes
* Stage functions may be reversed on earlier revisions.

V7-10
EL84 Russia



------

Okay, now what does that mean and which tubes should I buy? :embarrassed:
 
telecaster911 said:
What is the amp doing that you need tubes?
Click to expand...

The clean channel seems fine, but the dirt channel has NO dirt at all. If the gain is maxed out it just hisses and crackles. Considering the amp was used when I bought it a few years ago, it seems like I might just want to swap them all out at once, right?
 
Kerouac said:
The clean channel seems fine, but the dirt channel has NO dirt at all. If the gain is maxed out it just hisses and crackles. Considering the amp was used when I bought it a few years ago, it seems like I might just want to swap them all out at once, right?
Click to expand...

That could be a larger issue. A tube change might be in order, and would be part of the troubleshooting process. You should have a spare set of tubes anyway. But it might not be the tubes at all. Could be one of the pots.
 
Help!I'maRock! said:
That could be a larger issue. A tube change might be in order, and would be part of the troubleshooting process. You should have a spare set of tubes anyway. But it might not be the tubes at all. Could be one of the pots.
Click to expand...

I thought of that, but there doesn't appear to be any crackling on them. I just push in the gain switch though and FIIIIIIIIIZZZZZZZZZZ. Maybe I'll shoot a video of it when I get home tonite.

Tube recs would be welcome anyway. I haven't changed a set since my old Vibrochamp in high school, which had NOS ones. :(
 
Thread title offers an excuse to type Fee Waybil. That is all. Carry on.

Sent from my Transformer TF101 using Tapatalk
 
Maybe tap on the preamp tubes with a pencil while on the gain channel. It might show you which one is wonky. It doesn't sound like you need power tubes right away.
 
telecaster911 said:
And the 5ar4 is ok. Just play with the 12ax7's. Do you have any to try?
Click to expand...

Maybe. I assume I have AX7s in my '68 Bassman, but I haven't opened that one up to take a peek since I moved to the house. I'm pretty sure it still has it's ORIGINAL preamp tubes and maybe power too.
 
Here is the sum of my tube amp knowledge:

1. 6_6 = American
2. EL__ = British
3. HIGH VOLTAGE!
4. There are tones of other tubes that are higher/lower gain versions of #1 and 2, but they've got different letters and numbers.
5. 12A_7 are preamp tubes in other high end audio gear.
 
12AX7, 12AT7, 12AY&, et.c are all dual triode tubes...two triode tubes in one envelope. Each half is completely independent of one another

V1= 12AX7
V1A=2nd gain Drive channel
V1B=First gain stage for BOTH channels. This is also the most important tube for noise, anything introduce here gets amplified by the rest of the circuit. The signal goes through this triode and THEN is sent to the channel split.

V2=12AX7
V2A=Tone Control Driver
V2B=3rd gain stage for Drive channel

V3=12AX7
V3A=2nd gain stage for Clean channel
V3B=Reverb return amplifier*, amplifies signal returning from reverb tank

V4=EL84 reverb driver. A reverb circuit has a "power amp" complete with power tube and output transformer...on the old outboard Fender Reverb Units, this is a 6K6GT (6V6GT on the RI's); on the Fender reverb combo amps (Super Reverb, Twin Reverb, etc.), it's a 12AT7; on yours it's a EL84. Fender/Zinky also used an EL84 reverb driver on the Fender VibroKing

V5=12AX7 phase inverter tube. Each triode handles half the signal (positive or negative ends of the sin wave) and feeds it's respective power tubes. This is a high stress position, a 12AX7's will add more distortion and be able to pass clean signal onto the power tubes less efficiently that a 12At7 or 12Au7 which are higher current tubes.

V6= 5AR4/GZ34 Recitfier tube converts the high tension AC from the power transformer to DC for applying to the plates of tubes

V7-V10= EL84 power tubes. There should be a Class A/Class AB switch, this is actually a cathode/fixed bias switch.

The 12AX7WB is a Sovtek tube. The Chinese 12AX7 was a favorite for high-gain amps for a long time because of other tubes tendencies to go microphonic. Back when the early Pitbulls were made, there were a LOT fewer options for 12AX7 (Sovtek WA or WB, Chinese or JJ). Now there are dozens and you can feel free to pick and choose your favorites are at recommendations of others.

Kerouac said:
Here is the sum of my tube amp knowledge:
1. 6_6 = American
2. EL__ = British
Click to expand...

Total misconception. The amp is voiced by it's tone stack, I could build a Super Reverb that ran on EL34's and Marshall DID build amps using 6L6's and you would never be able to pick it out of a backline. Companies used the tubes they did because they were easier to source in their nation.
 
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Wyatt said:
12AX7, 12AT7, 12AY&, et.c are all dual triode tubes...two triode tubes in one envelope. Each half is completely independent of one another

V1= 12AX7
V1A=2nd gain Drive channel
V1B=First gain stage for BOTH channels. This is also the most important tube for noise, anything introduce here gets amplified by the rest of the circuit. The signal goes through this triode and THEN is sent to the channel split.

V2=12AX7
V2A=Tone Control Driver
V2B=3rd gain stage for Drive channel

V3=12AX7
V3A=2nd gain stage for Clean channel
V3B=Reverb return amplifier*, amplifies signal returning from reverb tank

V4=EL84 reverb driver. A reverb circuit has a "power amp" complete with power tube and output transformer...on the old outboard Fender Reverb Units, this is a 6K6GT (6V6GT on the RI's); on the Fender reverb combo amps (Super Reverb, Twin Reverb, etc.), it's a 12AT7; on yours it's a EL84. Fender/Zinky also used an EL84 reverb driver on the Fender VibroKing

V5=12AX7 phase inverter tube. Each triode handles half the signal (positive or negative ends of the sin wave) and feeds it's respective power tubes. This is a high stress position, a 12AX7's will add more distortion and be able to pass clean signal onto the power tubes less efficiently that a 12At7 or 12Au7 which are higher current tubes.

V6= 5AR4/GZ34 Recitfier tube converts the high tension AC from the power transformer to DC for applying to the plates of tubes

V7-V10= EL84 power tubes. There should be a Class A/Class AB switch, this is actually a cathode/fixed bias switch.

The 12AX7WB is a Sovtek tube. The Chinese 12AX7 was a favorite for high-gain amps for a long time because of other tubes tendencies to go microphonic. Back when the early Pitbulls were made, there were a LOT fewer options for 12AX7 (Sovtek WA or WB, Chinese or JJ). Now there are dozens and you can feel free to pick and choose your favorites are at recommendations of others.



Total misconception. The amp is voiced by it's tone stack, I could build a Super Reverb that ran on EL34's and Marshall DID build amps using 6L6's and you would never be able to pick it out of a backline. Companies used the tubes they did because they were easier to source in their nation.
Click to expand...

Wow, thanks! That was very helpful. Do you have any particular recommendations?
 
Kerouac said:
Wow, thanks! That was very helpful. Do you have any particular recommendations?
Click to expand...
As far as 12AX7 types, I like the JJ ECC83s and ECC803s, depending on where you want your mids and how much gain you want. The 83 is a bit gainier while the 803 has a bit more mids and a little less gain.

I also hear good things about the Mullard and Tung Sol reissues.
 
Kerouac said:
Wow, thanks! That was very helpful. Do you have any particular recommendations?
Click to expand...

Nope, my knowledge of modern preamp tubes is limited. I have enough NOS to hold me over for now.

But most people strongly suggest the newest Russian models...New Sensro went to a spiral filament with the 12AX7LPS, and then keep evolving this design into the 12AX7EH, The Tung Sol "reissue", the GOld Lion "reissue" and the new Svetlana. Some of these are even the same tube. But those last three, Tung Sol, Gold Lion and Svetlana get the most praise these days.

By the way, none of these spiral-filament tubes should be used in cathode-follower positions on Marshall, Voxes, Tweed Bassman, etc, but the Pittbull doesn't use a cathode follower stage.

Here are evaluations from the man who designed your amp (I do not know when this was done)...
Recently evaluated tubes:
12AX7A/7025 Shuguang
Well balanced tonal spectrum, low noise with moderate microphonic tendencies, easily selected out in production. Excellent for clean and overdrive sounds.
12AX7WB Sovtek
Lower gain, somewhat less bass response, and not as bright as Shuguang, but not dull sounding. Very low microphonic tendencies.
12AX7A Tung-Sol
Very good gain and low microphonics. Nice low end. Somewhat forward in the upper mids. Basically a fatter higher gain EH 12AX7. Appears to be an EH with a different getter.
12AX7 EH
Very good gain and low microphonics. Less low end than Tung-Sol and not as smooth on top. More pronounced in the upper mids.
12AX7LPS Sovtek
Similar to the EH but generally a little less of everything. Nice balance and a good alternative to the Shuguang if you like less top and a little more mid.
12AX7/ECC83 JJ
Works well in Valvulator 1, which was surprising, since it did not fare as well in prior testing. Apparently the hum and microphonic issues have been addressed. A little darker sounding than the WB.
When used in the amplifier V1 stage, this tube performs similarly to the WB, but the mids are more pronounced, the top end is dullish and overall somewhat harsh sounding for high gain settings.​
 
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