Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: gsb on May 02, 2020, 10:44:44 am
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Hi,
I,m new on forum,was reading forum some years but was not active.My interest is now on TBMeister .Last year i have build cabinet for friend-blues player.He heard some files from Tubenit and Geezer ..... must have .... I would like to build first a test amp (have small Hartke chassis from old ss-amp) make all tweaks an after that make a clean build in new chassis.For first i have set of transformers from german winder Shinrock for jtm45 amp.Output transformator with 8k primary and 4,8,16 ohm taps.Power transformer is center taped with secondary windings 325v and 350v .Choke is also included.Player wants good clean tone,used mostly digital reverb (t-REX) in front compressor and some OD pedals.My idea is clean channel with 12ay7 ,Fx active,OD,.I would use cathode bias 270ohm ,KT 66 on outputs (8K primmary) there be posible to use JJ 6V6 also (330 ohm cathode resistor).For start i will go with solid state rectifier.For caps i have ordered some Jupiters and Orangedrops 6ps for OD,715 forPI.For plates i have odered some Dale rn65 resistors. There are some sugestions for output caps 0,022 or 0,033 ? How is to use KT 66 in this amp? Two independed master volumes (clean ,OD )will be fine .In some schematics i have seen VVR for power section -is there big influence on sound ? Thanks for help
gsb
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I would like to build first a test amp (have small Hartke chassis from old ss-amp) make all tweaks an after that make a clean build in new chassis.
I suggest to leave the transformer leads full length for the test amp. Wait to trim to length when you build the final amp.
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I would NOT use VVR for the amp. I'd go with a master volume as in the schematic you posted OR a PPIMV (if you want that).
I did not find the trim boost useful on my TBM & removed it. On the OD channel, I'd recommend a 250ka Level pot (this is just my personal preference to acquire the tone I want).
IF you install an active FX loop, you may not need a "master volume" at all because the FX loop will function as a master volume.
There is a Matchless amp that uses KT66 cathode biased. It has a separate resistor/cap for each cathode of the power tube. I'd give that approach some consideration.
I liked .033 coupling caps post LTPI, but that's not necessarily better just a preference.
Here are some of DaGeezer's TBM soundclips:
overdrive high gain
https://soundcloud.com/dageezer/higainnoodles-on-the-bm-01032011mp3
clean tone
https://soundcloud.com/dageezer/noodles-on-the-bm-01032011mp3
I'd think one would be hard pressed to get a better tone then DaGeezer's TBM.
With respect, Tubenit
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Hi,
Thanks for advices ,yes i will leave transformer leads full lenght.I have seen another schematic for KT66 cathode bias -with two separate resistors 540 ohm.How is with bypass cap -two 25micro/100V caps must be fine.No it is no need for ppimv.Your fx -loop is close to dumbleator is there any advantage with parallel function ? Ok i will instal 0,033 caps on PI.In Juanjo version there is 12at7 -stay longer clean - i think ? There are also two diferent NFB schematics.I think i will build OD with tone betw.OD stages.
thanks gsb
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No advantage of parallel that I can see just a personal preference for me.
I found I preferred the OD tone control between the OD stages also. The attached schematic is what I eventually ended up with after trying tweaks for several years. NOT saying this is what you should do. It's simply what I preferred.
I like a fairly clear OD tone that is not distorted & found a lower drive pot value of 25kl worked OK for me for the tone I wanted. The 200k plate resistor was simply cause I ran out of 220k resistors.
with respect, Tubenit
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Hi,
Thanks,Tubenit for really helpfful advices.Player plays relative clean with not so much OD -distortion.Goal is good sustain ,and bloom,super clean sound is on the first place.
First I build Fx standard as in the schematic-I have read in previous posts fx add some bloom to sound.
Thanks for help
gsb
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IF I were building a Tweed BluezMeister for a friend and they wanted a great clean tone and a smooth clear OD tone with an active FX ………………. this is what I would build based on tweaks I've experimented with.
NOT saying you should do it this way! Simply stating some of my preferences.
In the clean section:
1) I used a mini-toggle to go from a mid-scooped tone to a fatter mid-thick tone.
2) The original PAB, I did not like at all and didn't use it because it was too big of a volume jump and was harsh.
This PAB has a mild volume jump and to my ears, is quite smooth.
In the OD section:
1) I found I like the OD tone control between the OD gain stages and not after. Smoother and more efficient to my ears
2) I found I did NOT like the OD drive turned up very much. It gave too much of a distorted tone. So it became a
"set and forget" pot to me. I think a 50KA is better suited.
In the FX section:
1) When I measured the original FX send pot, I found it was typically set with less then 25k to ground, so I went to a
25ka pot
2) I like the paralleled FX, but that's again just a preference.
3) I found the FX return pot was a "set and forget", so I began using an 82k resistor to ground. You could go down to
39k, I think?
These are all just preferences I have for your consideration. You may or may not like them. I attached an editable ExpressSCH version for you.
With respect, Tubenit
EDIT: I added a layout for this schematic. Compare with schematic. IF there is a discrepancy, go with the schematic.
CHECK for ERRORS!
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Hi,
Sorry Mr.Tubenit for late response (heavy duty job int.care-hospital ) .Your information was great inspiration for my project.
FX section:
-for test amp i will build 50k and 100k pots in to see how they acted with digital reverb/ delay from player.I think parallel as in the schematic will be ok for me.
- Tube : 12 ay7 or 12u7 ?
OD section:
- OD ps caps ,Dale rn65 on plates ,Tube 5751 ok,i have also some 12dw7 tubes i have put some on Hotrod deluxe OD channel they work fine..
Clean:
- fat thicker tone yes.. :m8 versus scoop best off both Fender/Dumble -player plays some fine guitars (Suhr /Fender custom ,ES355)
- mild volume jump is ok ,
- mid boost 710p ? -some previous scematics 390 ?
- Caps all Jupiter or better mix with OD 715 or PS ..?
On power amp :
10 k grid -for KT 66 ?
- for screens i have 1k/3w they worked good in hotrod deluxe pimped with kt66
- on John Mayer amp i have seen -countur pot -Cut - is there any need for that .
- NFB any mods recomended ...or better leave as is..
- I used solid state rectifier UF5408 diodes and evt.sag resistor to emulate tube rectifier .
THANKS for your support
gsb
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GSB,
These Dumblish inspired amps should be considered a foundation recipe that you season to match your personal taste for tone. I think you'll have to experiment with the amp components brands and some of the component values.
I think the Jupiter or OD-PS caps are fine. I think the Vishay-Dale RN65 resistors are fine on the plates. I experiment a lot with tubes 12AX7, 5751,12AT7, 12AY7, 12AV7 and 12DW7 and reverse 12DW7. IF you want a cleaner tone use a 12AY7 V1, 5751 V2 and 12AT7 V4. IF you want more overdrive, use 5751, and then all 12AX7's.
The schematic I posted for you is simply my personal taste after experimenting and finding out what works best for me.
With respect, Tubenit
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Hi,
Thanks Mr. Tubenit for nice advices. I know is a individual taste how the amp sounds. Last year have tune up hotrod deluxe and have think it will be quick pimp and at the end I have pulled pcb 3 times out.. How works ppimv for this amp? I will report about progres..
gsb
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How works ppimv for this amp?
The PPIMV will work with this amp, but as you turn down the PPIMV …….. it begins eliminating the negative feedback.
IF you use an active FX loop, then I don't think you "need" a PPIMV. However, even though you may not need one, you might prefer the sound of having one.
With respect, Tubenit