Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on September 12, 2011, 08:23:56 am
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I was looking at the PI last night at the resistor values. I found a 2.7K in place where a 470 ohm resistor would be. I replaced it with a 470 ohm and the amp has more headroom now. But the breakup that i had is less. Has anyone ever seen a 2.7K used in the PI like this before?
Would the higher resistor value create more breakup? It's Monday!
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You might checkout TUT3 by KOC. Maybe it's one of O'Connor's mods to this amp. Meanwhile checkout the schematic of the EL-84 version of the Traynor Bassmate YBA-2B. The PI's are very similar, but the Bassmate has no NFB. It seems that the same basic PI circuit was made a bit more complex to accommodate the NFB loop in the Guitarmate. The stock 470R resistor is in series with a total cathode resistance of about 10K or 15K in those amps. Hence it seems to me that changing the 470R to 2.7K, a net increase of about 2K2, is a reasonably small percentage change in the overall cathode resistance.
However, it also affects the amount of voltage division in the NFB circuit. It appears that the NFB is fed both: a) into both cathodes of the PI, and b) into the lower half's input grid. Because the change in the value of this resistor alters both the final NFB voltage AND the bias of the tube, it is beyond my pay grade to compute the combined results, except for trial & error with different component values.
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Thanks jjasilli i will check out that Bassmate schematic. I didnt catch my eye earlier. This may explain a problem i found when i tried to change the feedback resistor from 100K to 820 last week. The 820 would not allow any sound from the amp. I simply tried an 820 and got no sound. Dmdest thing ive seen before. I put the feedback back to 100K. Was just trying out different changes here and there. The first stage copling cap to the volume was changed from .1 to .01 / What a nice difference. You can make this amp do just about anything you could want. The EQ is awesome
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The EQ is awesome Cool! But for reasons unknown to me, some people are unhappy and mod the tonestack. The Guitarmate I worked on already had the tonestack modded. It sounded good so I left it that way. FIY: My thread on that amp is here: http://www.el34world.com/Forum/index.php?topic=6675.0 (http://www.el34world.com/Forum/index.php?topic=6675.0)
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Gona read your thread now. I have read about people moding the EQ but i dont see how it could get any better that it is. Other than changing the first stage coupling cap from .1 to .01 / The amp is as close to GOD in a box as i could ever dream of having. How can it get any better?
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jjasilli after viewing both the YGM-1 & YGM-3 schematics i have the following:
The preamp is all YGM-1 values. The PI and power section coupling and bias is YGM-3
The amp is all stock and a solder iron has never been put on the board (before now) :dontknow:
The parts are all original and old like me
It's no big deal except for i am trying to figure out where the H this amp came from or was it a Traynor techs personal preferences
The tube chart says YGM-3 but has a 12AU7 tube on the chart as is in the first stage of the YGM-1
That 2.7K LTPI resistor is freaky
My slope resistor is the YGM-1 100K. Im going parallel an 82K and get near your 58K in the mods you have done
I changed the V1 100K plate to 220K as in the YGM-3. Im turning it on now to see how it sounds
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That 2.7K LTPI resistor is freaky Yes it does look like Traynor original!
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God in a box?
I've never heard anyone describe a YGM-3 in those terms before. I've worked on many of those amps and while they sound quite good,none even comes close to my own builds in terms of tone.If they were so awesome the new Hand-wired Traynors would be selling like hotcakes.But they are not.They sit in the store here and collect dust.The prices are quite reasonable too.
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God in a box?
I've never heard anyone describe a YGM-3 in those terms before. I've worked on many of those amps and while they sound quite good,none even comes close to my own builds in terms of tone.If they were so awesome the new Hand-wired Traynors would be selling like hotcakes.But they are not.They sit in the store here and collect dust.The prices are quite reasonable too.
I dont know. Theres something very spicy going on with this amp. After i made some resistor changes to the reverb to tame it a bit it got even better. Seems to have a bit more headroom as well. It sounds like a deluxe reverb and a 25 watt Marshall combined depending how the EQ is adjusted. Im running it through a 2x12 1963 Cordovox cab with some old 70's no name speakers. Beat to H but i get good comments all the time on the sound of the cab. The amp is not back in it's cab yet. I know the single Marsland speaker cant handle this amp
Heres a youtube video of of a slightly modded YGM-3. It sounds pretty good. What gets me is the EQ can dial in anything. JMHO
The playing begins at 4:35
Traynor YGM3 amp mod Part 3 (http://www.youtube.com/watch?v=IOsBoIpqVMo#)