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PostPosted: Tue Apr 10, 2018 7:29 pm 
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Bottle Rocket

Joined: Sun Apr 08, 2018 12:58 pm
Posts: 13
Hi everyone,

I've had some issues with my Subway Blues, mostly with the reverb (found out the Reverb Driver Tube (V4) was dead so that explains it), and the expected volume swells, hiss, crackling and popping sounds caused by worn-out preamp tubes. Power tubes need changing so I'm going for a full retube.

Now, my question is:
Are there any cathode follower tubes in the Subway Blues? And if so, which ones are they? I've heard V2 might be one but the info wasn't clear/reliable.

I know V1 isn't one, neither is V3 (Phase Inverter), but what about V2 and V4 (Reverb Driver)?

Last thing:
Which tubes are NOT suitable in the cathode follower position?

Thanks a lot for any help you can provide!

Chris


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PostPosted: Sun Apr 15, 2018 11:34 pm 
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Bottle Rocket

Joined: Tue Jan 03, 2017 10:16 pm
Posts: 20
Hello,

I cannot help you with which position is the cathode follower on this amp. I can advise about suitable tubes. Chinese made 12AX7s work well in this position they seem to handle higher voltage better than most Russian tubes. I have also heard the Sovtek LPS (long plate) is good as a cathode follower.

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PostPosted: Tue Apr 17, 2018 9:27 pm 
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Bottle Rocket

Joined: Sun Apr 08, 2018 12:58 pm
Posts: 13
Thanks.

About the Sovtek 12AX7LPS, I've read from multiple sources that they're not suitable for this application, due to its Spiral Filament construction, like the Tung-Sol RI, Electro-Harmonix, Mullard RI. Although the JJ ECC83S, while being a spiral filament tube, is supposed to work fine.

The general consensus is that Russian tubes from New Sensor are to avoid, except for the Sovtek 12AX7WA/WB/WC (info directly from New Sensor).

Anyone out there who knows how to read an amp schematics could tell me if there is a cathode follower tube in the Subway Blues?

The obvious spot is the one following the tone stack, but I remember reading about Mesa using a Resistor as part of the cathode follower circuit design in that amp, although I don't have the slightest clue as to what that could mean or imply. I really need your help guys!

I've had some issues with my amp, I need to do a full retube SOON because I need to use the amp at a wedding! And obviously I don't want to put something that will blow up while gigging, and I want to avoid using chinese tubes in this Vintage sounding marvel of an amp!


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PostPosted: Wed Apr 18, 2018 7:38 am 
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Single Recto
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If the available schematic is correct, there's no cathode follower in the Subway Blues.


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PostPosted: Wed Apr 18, 2018 1:03 pm 
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Bottle Rocket

Joined: Sun Apr 08, 2018 12:58 pm
Posts: 13
Thanks so much!

I had read somewhere that a resistor (from what I remember... might be more than just a resistor) did the job of the cathode follower in the Subway Blues' circuit, but since the source seemed sketchy, and I didn't want to risk blowing up a tube I would have just ordered, I wanted confirmation.

Thanks again! Now I can order the tubes I want, with peace of mind, and in time for my cousin's wedding gig!


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PostPosted: Sat Apr 21, 2018 3:20 am 
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Mark II

Joined: Sun Aug 07, 2011 12:17 am
Posts: 106
Location: Alkimos, Western Australia
I can't see the tube compliment in the Subway Blues user manual. What about the FX loop? I have the Rocket 44 which is related preamp-wise (part of the Subway family). In the Rocket (which has 4x12ax7s) V3 is a cathode follower tube and I have found that JJs get chewed up very quickly in that spot. I found out about the Chinese 12ax7 being a better option for that spot several years ago (from this forum).


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PostPosted: Sat Apr 21, 2018 6:30 am 
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Bottle Rocket

Joined: Sun Apr 08, 2018 12:58 pm
Posts: 13
I found out that the Q1 Resistor is used as a cathode follower to drive the fx loop in the Subway Blues.

One way to reduce both manufacturing cost and the price it was selling for.

Even if this trick was used to avoid using a tube to fulfill the cathode follower's function, which many tube purists might say it's heresy, the Subway Blues is in NO WAY lacking in tone or feel.

Now, that being said, I don't know if there would be a way to mod this amp to remove the resistor and add a tube to use as a cathode follower, making the fx loop truely "tube buffered" as Mesa advertised (which is false in this case).

And since this function uses only half of a preamp tube (12AX7's being double triodes), I have no idea how the other half could be used.

More so, I don't know if the amp would really benefit (enough or at all) from a tube cathode follower. Such a mod might not be worth it in the end...


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PostPosted: Wed Jun 27, 2018 11:17 pm 
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Mark II

Joined: Fri May 04, 2018 10:36 pm
Posts: 90
V2A is a cathode follower stage. It's the only tube cathode follower circuit in the Subway Blues amp. Don't use a Sovtek tube in that socket.

Get Mesa tubes. They're more likely to work right every time without guesswork than any other tubes you can easily get.


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PostPosted: Thu Jun 28, 2018 7:13 am 
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Single Recto
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woodbutcher65 wrote:
V2A is a cathode follower stage.


Do you have a schematic showing this?


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PostPosted: Thu Jun 28, 2018 12:21 pm 
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Mark IV
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woodbutcher65 wrote:
V2A is a cathode follower stage. It's the only tube cathode follower circuit in the Subway Blues amp. Don't use a Sovtek tube in that socket.

Get Mesa tubes. They're more likely to work right every time without guesswork than any other tubes you can easily get.


This is completely inaccurate. Aside from what has been mentioned regarding the effects loop, there is no cathode follower circuit in the amp.

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PostPosted: Thu Jun 28, 2018 3:23 pm 
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Mark II

Joined: Fri May 04, 2018 10:36 pm
Posts: 90
I swear I saw a cathode follower stage in V2B. :shock: Was I even looking at the right schematic?

I sure know what they look like on a schematic and how they work. Well, increase that cathode resistor on V2A to 100K and jumper out the resistor between V2A's grid and V1B's plate and it would be!


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