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  Speaker blending in symmetric stage setups
Posted by: physics - 01-28-2023, 06:00 PM - Forum: TUT Q&A - Replies (1)


I finally have a chance to try out symmetric stage setups in a band context. However, all of the cabs will have different speakers or speaker blends due to what speakers I own and can load into the cabs, impedance concerns, and what is already loaded into the other guitar players' cabs. I wanted to ask if any of you can provide advice on how speaker blending affects the outcome of symmetric setups. My guess is it would be optimal for either two cabs per player that are different but complimentary, or for two that are as similar as possible. For the former, experience with recording and mixing different complimentary speakers would seem to imply that a fuller sound would result. However, the psycho-acoustic effect mentioned in TUT where the listener/player feels like they're in the sound because of two separated sources would seem to imply that the more difference there is between the two cabs, the less they would be sources of the "same" sound and thus the effect might be weaker.

Technical details, if it matters:
The cab pairing is going to be a 1x12 in parallel with a 4x12, and a 2x12 in parallel with a half-empty 4x12. The 2x12 has a eminence swamp thang and celestion g12h 70th anniversary, wired in parallel for 8 ohms net. The 1x12 has a 16 ohm Celestion 70-80. These two cabs aren't mine, so I am not able to control the speakers loaded in them.The speakers I own and can load into the 4x12's (which are mine) are 1x16 Ohm Vintage 30, 1x16 Ohm Marshall G12 Vintage, 4x16 Ohm Peavey Sheffield 1290. The 2x12 cab will be paired with the half-loaded 4x12, and the 1x12 with the fully-loaded 4x12, because of impedance concerns.

There aren't too many permutations possible, so worst case I can probably try all the options in a band context and see how it sounds, but I do wonder if there are any general guidelines for this beyond just separating the cabs.

Thanks for any input!

P.S. Here's a video showing and comparing the three speakers I own. It inspired the selection of the speakers I now own.

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  Thoughts on variable NFB control in Fender Bandmaster57-Style PA
Posted by: dtbradio - 01-02-2023, 06:31 PM - Forum: Personal Projects - Replies (2)

Hi All!

I'm currently working on my third amp project. Its basically a JCM800-type front preamp and tone stack coupled with a Fender Bandmaster57-style power section, with a few minor alterations. The Bandmaster has fixed NFB using a 56K into the cathode of the 1st PI tube, with a 5K-ohm and .1uf presence circuit. I'm using 3.3k on that cathode, and am going to try a variable NFB circuit using a 68K fixed resistor in series with a 50K variable resistor on a switch to allow either adjustment or elimination of the NFB. The presence control I've selected is using a 50K variable instead of the 5k used by Fender, basically for more range of control.

I'd like any and all opinions of those changes to the basic Fender circuit. Thanks in advance for all replies!

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  LPSP settings
Posted by: sinusoids - 12-30-2022, 02:17 PM - Forum: TUT Q&A - No Replies

I'd like to know how others set their LPSP.  Any comments on the application would great. 

My most used amp is the LPSP driving the PA in ToT (similar to a fixed bias 5E3 PA with MV) with 6V6s.  I play an SG with P-90s with vol between 9 and 6, mostly on the neck.  This amp is played with a band so is set bright to get through.  I use a pedal for vol boost on leads so the two channels are used for 2 rhythm tones.  So vol is roughly the same for both channels.

             V    H      M    L     D
Clean    5     8     1.5  5.5
Lead    3.5   8.5   4   4.5  8.5

26 years ago today I purchased TUT at Antique Elec Supply in Tempe.  Thank you Kevin, for publishing these, sharing the info and answering SO many questions. 26 years of fun.

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  Hello all
Posted by: Darth-Apple - 12-25-2022, 05:19 PM - Forum: New Member Introductions - Replies (2)

Hello everyone, 

I'm Darth-Apple, from east coast USA. I'm a lifelong musician and somewhat of an electronics hobbyist (not an expert, probably far less knowledgeable than most of you all. Tongue

Figured I'd join this community and say hi!

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Big Grin New from Atlanta!
Posted by: TheCrunchGuy - 12-12-2022, 12:12 AM - Forum: New Member Introductions - Replies (1)

Greetings Amp aficionado's! I'm Rick. Guitar player, AV design engineer and DIY pedal and amp mod/tinkerer. Thanks for having me. Look forward to learning and helping others as well.

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  Output Transformer Primary Impedance Affect on Tone
Posted by: makinrose - 12-07-2022, 01:25 AM - Forum: TUT Q&A - Replies (4)

I was reading TUT4 (I think) that details various transformer set combinations for 50W amps.  With that section was statement about how some builders/players favor the sound of high impedance primaries over lower ones and visa versa.  I've experimented with different primary impedances 5E3 designs but I'm not sure if the difference in impedance was great enough to experience a big difference and I didn't do it with two amp sitting side by side. To my ears the higher impedance transformer seemed to sound little softer and warmer but that could have been my imagination. 

What has been other people's experiences? Also given the same supply voltage what effect should we expect between say a higher and lower impedance primary as far as tone? 


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  Basic Construction and Grounding Questions
Posted by: dtbradio - 11-23-2022, 11:32 PM - Forum: Personal Projects - Replies (1)

Hi All!

Happy Thanksgiving to all who celebrate that day tomorrow!

I'm in the process of building my first large tube project, a 3-tube amp built from junk-box tubes and parts just to make it interesting. I have a Marshall-style pre-amp section (minus tone stack for now, and with a few cap values different from Marshall because I don't have those exact values), followed by a single-ended 6V6 power stage. The power stage works great, plenty of volume into my home-grown 2x12 16-ohm stack using a pair of old Leslie 8-ohm series-wired speakers in an old Leslie cabinet. The problem I'm having is high-audio-frequency oscillation at high pre-amp gain levels which sharply drops over-all volume and exhibits a severely-compressed sounding tone. This issue goes away if I back off the gain. Master volume level changes don't seem to make any difference. My main question is this: should I be chassis-grounding everything, or isolate all circuit grounds from chassis except at one spot? My input jack is not isolated, but I have isolated the speaker output jack. I have noticed that if I keep the input cable short, the problem isn't quite as bad. I've also noticed that touching the amp chassis or metal on my guitars will alter the background noise of the system, IE hiss and buzz. My research has shown opinions in both directions on the grounding subject. I do know that my grid stoppers need to be relocated directly to the grid pins which I haven't had a chance to do yet. I'm also thinking of increasing the pre-amp stoppers to about 82K to roll off as much signal above 10KHz  as possible. I don't have the amp here at the time of posting, and I can't recall if I used a grid stopper on the 6V6. Thanks in advance for any insights!

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  TUT3 Portaflex
Posted by: Bassman - 11-18-2022, 07:58 PM - Forum: TUT Q&A - Replies (2)

Hi All,

New guy here.

I'm just testing a TUT3 Portaflex.
I've built some simple valve pre-amps and done some repair work on valve amps previously.

The Portaflex build went well (I'll post some pictures) and it sounds very good.  Loud, dead quiet, as well.

I have two questions,
1) The preamp seems to have quite high gain.  Putting the volume above 2 starts to get pleasant fat distortion.  Seems a little early.  Any advice?
2) What sort of voltages should I be testing for in the circuit?  Most of the published Ampeg Portaflex schematics have voltages indicated at the relevant points.

Woo Hoo!


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  New guy from UK
Posted by: Bassman - 11-18-2022, 07:47 PM - Forum: New Member Introductions - Replies (1)

Hi All,

I'm a bassist and equipment tinkerer from London (England).

I like to design and make preamps, amplifiers and effects.

Lately, I've been prototyping valve preamps, and working my way through the amps laid out in TUT3.

Very happy to be here.


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  Load Line Assistance Needed
Posted by: dtbradio - 11-10-2022, 10:57 AM - Forum: Preamp Mods & Design - Replies (2)


This is my first post on this forum. Fitting for a tube noob, lol! 

For my first question/problem, I need to be pointed to clear and concise info on how to plot a loadline for a tube. In particular, I have 12AX7, 12AU7, 12AZ7, 6K6, and 6V6 tubes around some of which I plan on building a guitar amp. I've been to several websites and done Google searches, but haven't found anything that truly cleared up the mud with regards to plotting load lines. My first BIG question is plate voltage. Do you use the unloaded B+, or measure it under a DC tube load?

Thanks in advance for any helpful replies!

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Come in where it's warm!
A warm welcome to tube amp modding fans and those interested in hi-fi audio! Readers of Kevin O'Connor's The Ultimate Tone (TUT) book series form a part of our population. Kevin O'Connor is the creator of the popular Power Scaling methodology for amplifiers.
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