Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jjasilli on May 05, 2009, 03:56:50 pm
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Seems to be Traynor season. Just finished-up with a friend's 1969 YGM-3 Guitar Mate. The schematic, showing changes is attached. This amp came to him from eBay previously modded. Of note, it was converted to Cathode Bias. A Weber Copper cap box had been installed and the filter caps replaced . The Trem was disconnected. The amp was pretty noisy.
The 2X 100K grid leak resistors to the power tubes had been replaced with a dual 100K ganged pot, residing in the trem intensity hole. The 10K resistor to ground after the bass pot was replaced with a 10K "mid pot" residing in the trem speed hole. These 2 mods were very IN-effective and were reversed.
Some of the noise was from old and failing tubes. I replaced all the plate resistors and B+ dropping resistors. Also I enabled the shorting feature on all 3 Input Jacks. (The grounding scheme is pretty disorganized, but I didn’t have to fool with it.) The amp is now very quiet.
1. Tremolo. Special thanks to Tubenit for his recent tremolo thread. After engaging in that, this restoration was a piece of cake. Pot & resistor values had to be tweaked to get good speed and intensity.
2. Vol & Tone. I do not understand this tonestack or the mods to it. Seems to be a baxandall of some type. I drew the stock and modded forms for comparison. Anyway, it sounds good as modded so I left it as found. Except: I added a 10pF bypass cap to the vol control. This really brings out the tone of the amp. Small downside: the vol does not turn completely off, but leaks a little at full CCW rotation.
3. Power Amp. I left the 100R screen resistors, a pretty weird value. The PI coupling caps were .047 and .022!!! So I made them both .047, one a mallory one an orange drop. But it sounds good.
4. Power Supply. Left mostly as found except I added the diode and the .22 Solens. That gives some extra filtering to the 3rd filter stage C, which feeds a lot of preamp sections. I like to put a diode in the B+ rail after the screen filter cap. It forces the power tubes to draw current for transient spikes from the AC outlet, and not from downstream stages. This is as-if the preamp and power amp were separate units. It increases touch sensitivity by giving full sway to transients.
And thanks to Doug for parts & quick shipment.
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If you're completely done with tweaks,restoration or mods .......... can you put an entire schematic drawing into the SCH files, please? I don't think we have any Traynor stuff in there?
http://www.el34world.com/Forum/index.php?board=12.0
Thanks for sharing what you've done.
With respect, Tubenit
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OK - new in the Schematics Section: a) this Traynor schematic is under a new thread; and b) just the tonestack is in your Tonestack thread.
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The tone action may be clearer if all drawn as top to bottom voltage-dividers. Or not.
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Yes, thanks! That makes much more sense. Based on your drawing I have further changed my drawings. The treble now clearly appears as a 3rd-order high pass filter; the bass circuit as a 3rd-order low pass filter.
EDIT: Whoops had to correct the re-draw of the modded circuit to connect the input of the treble pot in parallel with the feed to the first 250pF cap. It now looks like the treble pot and first cap also form a variable bandpass or notch filter. Also, in the bass portion, the cap > resistor > ground form a resonance filter. So it's not a simple 3rd-order low pass. Anyway, the general circuit is much more clear now.
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> it's not a simple 3rd-order low pass.
I don't think it is 3rd-order anywhere.
Confirmation: the steepest slope is ~~10dB/oct or 1.5-order, and most slopes are simply asymptotic to 6dB/oct or first-order.
I see it as two channels.
The treble is low-cut twice; except that first low-cut is "spoiled" by the large pot resistance unless you are at the extremes.
The bass is high-cut twice; except that first high-cut is variable-frequency due to the large pot resistance off the extremes.
You would naively expect simple flat, high-shelf, low-shelf.
However with multiple R-C networks you get enough phase-shift that simple addition of amplitudes does not give the right answer. The "overlap" zone could add, but in fact in this case it cancels. Hence the deep dip at some settings. This is a recurring theme in guitar amps: the classic Fender stack does it at some settings, and Gibson sprinkled twin-Tee filters liberally.
The "10dB/oct" happens only on the edge of this dip. It is possible there is a setting which gives "infinite" dip, and infinite dB/oct over an infinitely narrow band. But I think the steepest slope you will "hear" is a 200Hz fundamental suppressed 28dB, its 4th harmonic down only 7dB, a >20dB boost of the 4th harmonic, which will sound like "all harmonic no fundamental". Which is not a natural guitar sound (unless you damp a node on the string) but is standard among the conical bore wind instruments.
I think it generally covers the same ground as the Fender, with a few more parts, but more same-value parts, which could be cheaper in small production (if you build 5,000, then one 10,000-crate of 0.0047u is cheaper than two 5,000-crates of two different values).
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Yes, T-Filter is more apt.
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I see this is quite old, but thought I'd ask about values. What did you change the pot and resistor values to for the tremolo circuit? I'm looking at tweaking my YGM 3 a bit so that the tremolo slows down to usable levels. I basically have to play it slowed down all the way on most anything I use it on.
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Values are in the schematic attached to the first post in this thread. Intensity is nominally a 1M pot paralleled with a 1M resistor = 500K. But I think the actual reading was about 780K. Speed is 3M followed by R32 = 220K to ground.
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hey thanks for explaining dude, sorry I'm a newbie. I tried to open the schematic before I posted, but don't know what program I need to open the file. Searched to no avail.
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I tried to open the schematic before I posted, but don't know what program I need to open the file.
read this...
http://www.el34world.com/Forum/index.php?topic=500.0
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I just found one of these for sale on the island, a definite surprise and it sounds good, but I will go through it and make it sound killer. Threw some cash to hold it and will get it after the 1st. The Hi pass switch is way too much, but a simple mod me thinks.
It is pretty quiet gigging land here, so I am debating a MV for it, and possibly a Mid control, put on the back panel or a box to chassis addition. It has a Celestion in it and sounded pretty quiet in the store, trem and reverb in good order, but could sound even better. Might have been the cheezy tele clone I was handed to test it with. A good excuse to get back into amp land again. My work shop moved and never got back to proper organization. The three amps I have are working nicely, and once this one is tweaked, time to finished the Marshal 18w.
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Well have had the YGM-3 in hand for a few days. a bit more rough than initial expectations. Someone did some odd mods inside, like disconnect the tremolo foot switch, and wire the plug to volume pot and an resister after stage one. I think they wanted a direct out.. but...
It must have been set up for 220v here, because the PT is cranking out juice.
I have 406cv on Plates and 403v on shield -17.5 idle on grid
and every where else running about 15-20% hotter than schematic.
I am thinking it needs to drop, the EL84s are glowing too much.
And maybe lower the filtering to make it a bit more squishy.
The reverb is sounding worse and I am thinking to pout in one of my
other unused Accutronics spring pans to replace the one attached to the chassis.
The speaker is a 'Rola Celestion G12-30', no H etc. maybe a keeper maybe not.
The Vintage 30 sounds warmer in the other cab. I might swap it out.
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I have 406cv on Plates and 403v on shield Shield = screen?? Those are normal voltages for Traynor el84 amps. No harm in dropping it though.
-17.5 idle on grid Actually that seems high = cold bias. I suggest you measure cathode current and calculate plate dissipation. BTW: the only YGM-3 I've heard in person was converted to cathode bias - it sounds great.
The reverb is sounding worse Traynor reverb is not for everyone.
the EL84s are glowing too much ??? Tubes are supposed to glow, but not redplate.
Accutronics spring pans to replace the one attached OK, but note impedance matching. This Traynor reverb is cathode, not tranny, driven and needs the correct input impedance -- not the Fender value.
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It's not red plating, but on the edge. Screen, yes.
The old Mullards seemed ok, but swapped in a match set of JJ's
and also have a matched set of TADs to try too.
I am comparing the red to the Mullards, and it is much less,
but I have read the older tubes tolerate higher plate V than many newer ones,
and or modern wall voltage is higher these days.
The reverb sounded OK at first so, maybe that tube went bad.
Any clue about determining a spring reverb impedance? Meter?
Haven't changed that yet.
Put a new Mullard in V1-2 and a NOS RCA in the PI.
Running cold is possible, certainly. I'll have to crank up my old mac,
and get the calulation stuff transfered over.
Presence cap is gone for the moment.
Coupling cap 1 is now a Jenson .022
Fizzy cap went from 47pf to 100pf.
Speaker wires need replacing for sure.
A bit too late in my day to be terribly clear, 1am, for calculations.
I never work on amps when tired.
I do know at this hour that I will like this amp a lot when it's all sorted.
And the pop top cabinet is a tech's dream.
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http://roymal.tripod.com/accutron.htm
For reverb tank: There's a chart that shows nominal impedance AND the corresponding DC resistance you can read with a standard meter.
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Very cool JJ!
I have 3 pans
One is 9AB3C1B which is not listed, but close to.
9AB2C1B Fender/ Boogie 17" 6 10ohms/.81ohms 2575ohms/200ohms
maybe a stamp typo.
But you chart calls it:
type 9, Inp. 8 ohm, outp. 2250 ohm, long delay 2.75 to 4 sec,
input insulated, output grounded, non-locking, horizontal open side down.
And I do have a Fender matching transformer. So I can give this a go.
And I have two Belton BLBB1DIA Which I can't find anything at all about.
I found a Celestion G12 Heritage, that I had forgotten someone traded me.
Installed and sounding pretty good.
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And I do have a Fender matching transformer. So I can give this a go. Yes, you can convert to a Fender reverb circuit entirely. Personally I like Traynor reverb as a variation on a theme.
And I have two Belton BLBB1DIA Which I can't find anything at all about. If you take static (DC) resistance readings of its input & output, you can use the posted chart to ascertain its nominal impedance ratings. In other words those conversions are not specific to the tanks listed; and will work with any tank. I think you already realize that, but just in case.
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Always good to have confirmation of a method.
Thanks again.
I need to test/swap out the tubes, first
and maybe try a 12AY7 or 12AU7 also and see if it cleans it up.
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Been tweaking for a while now.
15k r @G and 10k pot on bias. Running JJ's at 26 / 27mw much happier.
.01 Mojo Vit. T on 1st coupling cap cleaned up the woofy bottom nicely.
Went from 22mf (actually measuring 32mf) to 150mf on V1b cathode.
Screaming now, a bit hot, maybe, but will gig with it tomorrow,
might drop it back to 50mf, but it has some nice preamp crunch,
and scads of touch 'clean to scream with the pick' now.
It's a Fernandes Strat clone so not a high output guitar.
R to 150k from 47k paralleling Treble cap
.0047 working against .01 cap in Tremolo speed
Reverb is still not touched. Tried a 12AY7, but the tank seems the issue.
All in all it's turning into the cool amp it should be.