New PRS MT-15 Where Would You Place These 3 Types Of Preamp Tubes?

[craigbeckta]

Hey everyone,

I just bought a new PRS MT-15 yesterday... Wow!

It has as much gain or more than my old EVH 5150 III 50 watt head.

I have three types of preamp tubes that I am going to use to replace the 6 JJ's
to try to tame the gain a little.

In what position would you place these preamp tubes?

I have 2 Tung-Sol ECC803s 12AX7 Gold...
4 ELECTRO-HARMONIX 7025EH...
1 TUNG-SOL 5751

I know that is seven...

I am guessing the 5751 should go in the V3 position to tame some of the gain.

Where would you place the EH7025's and the 2 Tung-Sol Golds?

Would the Gold Tung-Sol be better in V1 or the EH7025?

What about V2, V4, V5 and V6?

Where would you place them and why?

Thanks in advance.

Craig

 

[Toolmaster Of Brainerd]

Personally, I'd go tung sol V1 and put the 5751s in the two lead channel spots (I don't remember the numbering)

5 and 6 are effects loop and PI. Try them all and trust your ears!

Trying lots of combinations and trusting you ears is always the best way to go about these things.

 

[László]

Trying lots of combinations and trusting you ears is always the best way to go about these things.

I'd agree.

You're probably aware of the fact that the Tung Sols and EH tubes are simply modern Russian tubes rebranded with old US companies' names.

V1 will have the most effect on gain. It's the tube closest to the input. Believe it or not, the phase inverter tube also affects gain pretty strongly. That will probably be the last tube before the power amp.

One nice thing you might also know already, but if not it's convenient to know, NOS 12AT7s are far less expensive than NOS 12AX7s, and using them can also reduce gain.

 

[Deleted member 5962]

One nice thing you might also know already, but if not it's convenient to know, NOS 12AT7s are far less expensive than NOS 12AX7s, and using them can also reduce gain

Ditto for 5751’s the last time I checked, and those are usually better options than 12AT7’s.

 

[craigbeckta]

Thanks for your feedback everyone...

I tried different tubes in a number of different positions.

It was an interesting experiment.

I ended up with...

Tung Sol 12AX7 Gold Pin in V1 Clean & Lead
EH 7025 In V3 Lead
Tung Sol 12AX7 Gold Pin V4 Lead

EH 7025 V2 Clean
EH 7025 V5 Effects

JJ 8803 S in V6 Phase

I didn't like the sound of the 5751 in any position.

I found two Tung Sol 12AX7's in V1 and V3 to thin and bright.

The tubes in this order sounded smoother and more lively..

Tung Sol 12AX7 Gold Pin in V1 Clean & Lead
EH 7025 In V3 Lead
Tung Sol 12AX7 Gold Pin V4 Lead

The two EH 7025's improved the clean channel in V2 and V5.

Also the JJ sounded better in V6 than the EH 7025 or the 5751.

It is surprising how different preamps can change the sound of the amp in
different positions because people always say it is a minor difference.

I heard major differences, the JJ's sounded pretty good to start with but the final
configuration improved the overall sound quality of the clean and lead channels.

I am curious what old stock Mullard's might sound like...

What is everyones favorite preamp tube for the lead channel in this amp?

 

[Deleted member 5962]

I didn't like the sound of the 5751 in any position.

I don't think you said whether your 5751 was new or old. If it's new, I don't have much info on a Tong Sol 5751. If it's old, it might be shot. 5751 is a great sounding tube... if it's most models of old ones. I have a Jan and a Mullard and they are great in everything I've tried them in. And, there are other reasons I recommend them over AT and AY tubes.

Glad you found what worked for you! If you want to find a way to tame the gain a bit, as you indicated, find a nice NOS 5751 and try it in V3.

 

[craigbeckta]

It was a new Tung Sol 5751 and it really did nothing to improve the sound.

I preferred the 12AX7, 7025 or the JJ.

 

[Deleted member 5962]

It was a new Tung Sol 5751 and it really did nothing to improve the sound.

I preferred the 12AX7, 7025 or the JJ.

I figured. I haven't heard much about the TS new 5751s, but NOS 5751's are great tubes, and will reduce the gain with proper transconductance.

 

[andy474x]

Great project! I'm a big fan of replacing the preamp tubes in the MT15, or pretty much any amp, to fine tune the response to preference.

I actually just picked up a second MT15. I have one in my studio that I just wanted to leave hooked up to my load box for recording. They're so portable, loud, and sound great, that I grabbed a second one for a "go" amp, will likely be the one I take to gigs and otherwise leave it at my drummer pal's house in his basement practice space, and not have to lug an amp back and forth every time we jam there.

When it comes to V1 tubes in the MT15, I like the new production Mullard ecc83 a lot, and the Tung Sol 12ax7. Have also had great results with the JJ e83cc grid frame 12ax7 (not the common ecc83s) although I don't have any in mine right now. Currently I have the Tung Sol in V1 in my recording amp and the Mullard in V1 in my "go" amp. They both add a little clarity. Mullard V2 in the recording amp and Tung Sols in V3/V4, NP Mullard in the PI. Go amp has NP Mullard ecc83 in V1 and NP Mullard 12at7 in the PI, the rest are the stock JJ ecc83s. It already sounds quite good, but possible I may replace the remaining ecc83s tubes down the road when there's more tube availability.

The Mullard ecc83 and JJ e83cc are both favorites of mine in pretty much any amp. The Tung Sols I'm much less fond of in other amps, but they do work well in the MT15.

Believe it or not, the phase inverter tube also affects gain pretty strongly. That will probably be the last tube before the power amp.

One nice thing you might also know already, but if not it's convenient to know, NOS 12AT7s are far less expensive than NOS 12AX7s, and using them can also reduce gain.

I like the 12at7 in the PI in most amps, including the MT15 rather than the stock 12ax7. The gain reduction refines the sound. And, I'm more and more a fan of the NOS 12at7's, in my experience the new ones generally don't do it right. The only modern 12at7 I can honestly say I like is the NP Mullard. My PRS amps, for whatever reason, have been very finicky about modern 12at7's, they're wildly inconsistent, sometimes microphonic as a reverb driver, and in the PI sometimes sound just plain bad, nasty breakup character. I'll take a $20-30 NOS 12at7 over anything, except the new Mullard being quite good, too. Granted, I think this may be something localized to PRS amps, at least the ones I have, because I don't hear about it being a common issue. But, getting an NOS for basically the same price as a new production, it's a no brainer.

 

[craigbeckta]

Thanks for all of the tips.

 

[László]

I think it's great that you rolled tubes like this!