T-Rex clean channel (X2)?

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Ampman5150
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T-Rex clean channel (X2)?

Postby Ampman5150 » Wed 07/10/19 10:15 am

I'm wanting to build a 18 watter inside an existing 5E3 cab keeping all cosmetics etc stock. (Lets call it a 'sleeper' amp)
So... wondering if its possible to eliminate V2 (from the 18 watt 'trex' schematic) and have 2 different voiced channels feeding the long tail PI?
My idea is to keep all 4 inputs and combine the channels similar to the 5E3.
Thoughts?
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Re: T-Rex clean channel (X2)?

Postby JMPGuitars » Wed 07/10/19 12:12 pm

Eliminating V2 on the TRex is no problem, but then it isn't a TRex anymore. You should probably start with the Lite IIb, and consider using both halves of the preamp tube as your two channels. Then you can decide what happens from there, and eventually end with each channel inputting at each half of the PI respectively...if that all makes sense.
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Re: T-Rex clean channel (X2)?

Postby Ampman5150 » Wed 07/10/19 11:10 pm

My problem with the Lite IIb is that it parallel's the anode of V1.
I'm going to guess that for extra gain to drive the long tail PI.
I was thinking of separating V1 with a 100K\1K8/10uF (a) with a 220K\2K7/.68 (b) and combining the 2 separate volumes (2 channel) similar to a 5E3.
I assume I wouldn't have enough gain to drive the concertina style PI?
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Re: T-Rex clean channel (X2)?

Postby crgfrench » Thu 07/11/19 12:43 am

Ampman5150 wrote:
Wed 07/10/19 11:10 pm
My problem with the Lite IIb is that it parallel's the anode of V1.
I'm going to guess that for extra gain to drive the long tail PI.
I was thinking of separating V1 with a 100K\1K8/10uF (a) with a 220K\2K7/.68 (b) and combining the 2 separate volumes (2 channel) similar to a 5E3.
I assume I wouldn't have enough gain to drive the concertina style PI?
If you build the concertina style (instead of a LTP) you will have another gain stage from the non-PI triode. That should work fine. My Fullerwell is concertina and separates V1 with a 100K\1K5/25uF-25V (a) with a 220K\2K7/.68uF-100V (b) and combines the 2 separate volumes (2 channel) similar to a 5E3. That feeds the gain triode of the second tube. Then the last triode inverts the phase. Works like a dream. Uses standard 5E3 tone setup too.
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Re: T-Rex clean channel (X2)?

Postby JMPGuitars » Thu 07/11/19 7:12 am

Ampman5150 wrote:
Wed 07/10/19 11:10 pm
My problem with the Lite IIb is that it parallel's the anode of V1.
I'm going to guess that for extra gain to drive the long tail PI.
I was thinking of separating V1 with a 100K\1K8/10uF (a) with a 220K\2K7/.68 (b) and combining the 2 separate volumes (2 channel) similar to a 5E3.
I assume I wouldn't have enough gain to drive the concertina style PI?
So separate it. Lite IIb is the starting point. You don't need to keep any specific thing the same. You'll likely want to experiment a little. Look at a few different schematics to get an idea of what you want that tube to look like. For example: storage/18watt_tmb_JAschematic.pdf
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Ampman5150
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Re: T-Rex clean channel (X2)?

Postby Ampman5150 » Thu 07/11/19 11:55 pm

I appreciate the responses..
My goal was to keep the stock chassis in tack.
This would limit my pre-amp section to one (1) tube that feeds the PI section (concertina = both sides of the triode V2)
Simply put... Can I marry a 5E3 preamp (V1) to the TMP (or TRex) PI?

Cheers
R
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crgfrench
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Re: T-Rex clean channel (X2)?

Postby crgfrench » Fri 07/12/19 12:44 am

Ampman5150 wrote:
Thu 07/11/19 11:55 pm
I appreciate the responses..
My goal was to keep the stock chassis in tack.
This would limit my pre-amp section to one (1) tube that feeds the PI section (concertina = both sides of the triode V2)
Simply put... Can I marry a 5E3 preamp (V1) to the TMP (or TRex) PI?

Cheers
R
yes you could do that. you could also marry the 5E3 preamp V1 & 2 to any 18W output section and rectifier. eg:
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Re: T-Rex clean channel (X2)?

Postby Ampman5150 » Sun 07/14/19 6:17 pm

crgfrench wrote:
Fri 07/12/19 12:44 am
Ampman5150 wrote:
Thu 07/11/19 11:55 pm
I appreciate the responses..
My goal was to keep the stock chassis in tack.
This would limit my pre-amp section to one (1) tube that feeds the PI section (concertina = both sides of the triode V2)
Simply put... Can I marry a 5E3 preamp (V1) to the TMP (or TRex) PI?

Cheers
R
yes you could do that. you could also marry the 5E3 preamp V1 & 2 to any 18W output section and rectifier. eg:
So... that schematic is not a long tail concertina PI and has an extra drive POT.
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Re: T-Rex clean channel (X2)?

Postby crgfrench » Sun 07/14/19 10:00 pm

"Concertina" PI is not a LTP PI.

"Concertina" is synonymous with Cathodyne, or split-load, PI.

The circuit I posted is a concertina PI rather than a long tail pair PI. The extra pot is a master volume pot; if you don't want a MV just replace it with a 1M grid leak resistor. This is the Tweed Deluxe cathodyne PI ("concertina"). You could use a 12AX7 instead of the 12DW7, wired as a LTP here if you prefer.
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