Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: m3moser on February 22, 2012, 01:20:37 pm
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Hi All- I had a spare chassis and head cabinet in the shop and I had been reading about the newest TOS II version, so I went ahead and built it. See a few pictures attached. I had built the first TOS amp and it came out nicely, so I wanted to try some of the new features this one had. Now that its built I have a few questions about what certain controls are meant to do and how they work in conjunction to other controls.
PAB is pretty straight forward and works fine. I had read that the Chime control was to be able to do a bit of tone tweaking while in PAB engaged mode. My chime control seems to do nothing in any mode.
Mid control- I moved this control to the faceplate and made it full sized. I also set the trimmer pot on the circuit board to approx the 39K called for on the schematic. I do not hear anything happening when the mid pot is rotated. It seems to have no effect. The mid boost feature (switch) works fine.
Normal vs. OD Channel- I think I would like a bit cleaner sound on the normal channel. When the PAB and Mid Boost are engaged, its certainly a classic rock sound on the clean channel side. I would expect to be needing to tweak the tone stack a bit to more fender blackface values? I do have a 12AY7 in the first spot as the schematic calls for.
I had a weber channel switching board on hand so I used this as my relay switch. I have not used these before, I always used the Dumble style relay and off board power supply rather than the 6V heater supply this board uses. It does seem a bit noisy but overall not bad and lower parts count than the Dumble style.
Overall I like the tone and sustain of this amp- especially the OD channel. Its a step closer to a Marshall sound to my ears than the Dumble overdrive circuit but that is not a bad thing at all. I used Mag Comp parts for this build. I think I used an output transformer they recommend for TW style amps and it sounds just fine with 5881 tubes. I wonder how this amp would sound if it was fixed bias...has anyone tried that?
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I had read that the Chime control was to be able to do a bit of tone tweaking while in PAB engaged mode. My chime control seems to do nothing in any mode.
The chime control is subtle. However, IF I switch the PAB on/off while playing you should hear a difference in tone. And if you turn the chime control you should hear a difference also. IF not, I'd try different values of caps there, maybe go smaller to a 330p.
Make sure that the chime is engaged (only) when PAB is engaged.
I play with the chime & PAB engaged the majority of the time and hear a smoother tone doing that.
I use a DPDT that switchs the PAB on and redirects the signal to the chime pot, simultaneously.Check to see for sure if yours is wired that way.
when the mid pot is rotated. It seems to have no effect
Not sure why the mid control pot isn't working for you? It doesn't work if the PAB is engaged, but should work fine with noticeable difference if PAB is off.
For my own education, are you saying the Weber relay is noisier than the typical Dumblish relay?
I think I would like a bit cleaner sound on the normal channel
Regarding a cleaner tone. Try a 120k/1.8k or 100k/1.5k on V1b
Glad you like the overdrive tone. I think it's somewhere between Marshall and Dumblish in tone.
GREAT looking build!!! IF you make sound clips, please post a link. THanks for sharing it.
With respect, Tubenit
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I can not tell how you have the mid pot wired? It looks like there is a possible resistor across the outside lugs?
Do you have it wired like in the schematic that I posted? The mid pot should be working for you IF the PAB is turned off?
with respect, Tubenit
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IF you decide that you don't want a "chime" pot, then you could use a dual gang 500k pot and approximate a Marshall tone stack instead.
You'd need to use a terminal strip for the MTS components. You could even consider soldering the terminal strip on the back of the dual gang pot. I have soldered terminal strips to the back of pots in the past successfully with a 40w soldering iron.
Again, it is important that the DPDT switch engages the MTS tone stack only when the PAB is also engaged.
With respect, Tubenit
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Thanks for the pointers. I will try to get the amp out onto the bench. There is one thing I did notice about the mid pot in the layout vs. the schematic. See the resistor in the layout on the pot? This is how I did my mid pot