evh0u812 wrote:I ended up removing the conjunctive filter. rolled some nos tubes trough the amp and found a set that sounded great without it. Besides mine was to be top mounted in its headshell and i didnt like the extra heat the 10w resistor was radiating.
Footswitch is a simple and useful addition. The core tone of the circuit is just stunning as youve found out. Mine shipped to the customer last week and i miss it already.
Did you use any screen resistors or stoppers at the output grids? Upon closer examination of my cranked tone I seem to be getting some blocking distortion, or something else that's making things a bit farty splatty fuzzboxy
No screens just grid stoppers. 5k6 from memory. Howled like a banshee without them.
Thanks, I put in 470r screens and 5K6 stoppers, but that didn't help the fartyfizz when cranked.
I tried Merlin's 1M stopper on the concertina grid and BOOM problem solved. smooth. I'll leave the other resistors in, they can't hurt. I did end up with 470K split on the cascade. I also found another(2 so far this week) crummy Bourns 1M, so I'm gonna replace all the pots in this amp, as they are all Bourns 1M. Bummer. It was actually adding noise to the amp at idle, somehow.
I changed the speed pot out for a linear 500k instead of the 1m with the 1m resistor over it.
Much nicer taper. The original pot did very little under half way....actually nothing.
Did you use the 0.47uf filter for v1? Such a crazy small value.....never did get around to trying more filtering.
Revisiting this amp I built 10 years ago (!). It has become my shop amp over the past few years with a great sounding Jensen blackbird alnico speaker. I ended up modifying over the years, and built an extra gain staged in front of the posted schematic. It's a thick, kinda dark amp, and sounds great with a tele. This was the amp I used to test the varistor substitutes Martin developed
Anyways, I'm gonna do a 6L6 version, but without the trem, just a bare bones version of the core of the amp.
Wat should I do with the trem 12au7 stages? I'm thinking just do the 18K stage into the cathodyne PI, but am looking for advice.
Thanks!
Magnatone213_zps770a9d3a.jpg
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sluckey wrote: ↑Wed Jan 03, 2024 10:49 pm
I would do this. Maybe change to an AC coupled cathodyne if not liking the DC coupled cathodyne. Only need 2 resistors and a cap.
Steve,
Do you know which Magnatone (or other) model that amp is that you posted the example of? The tone circuit looks interesting (as compared to a Tweed/18W type).
Thanks
EDIT: I see that is a 213 with the harmonic trem removed. I love the simplicity of that cathodyne (not many parts) but would think it would be wide open for frequency doubling problems?
Colossal wrote: ↑Thu Jan 04, 2024 12:55 pm
Do you know which Magnatone (or other) model that amp is that you posted the example of? The tone circuit looks interesting (as compared to a Tweed/18W type).
I just edited Smokebreak's schematic, but it is the Troubadour 213.
Here's a better schematic...
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Yea that tone control is neat, it acts as a mixture of cathode bypass on one side, and high frequency dump on the other, or a mix.
I think the overall sound of the amp is unique due to the combo of high Rp/Rk values on the unbypassed 1st stage. I put an added stage in front , on my amp, using a second input jack, and bypassed that stage's cathode, and put a volume pot in, and like that, with both volumes at noon and the tone dimed, it's amazing with single coils....it's kinda like a tweed 2203 or something....thus my want to build a bigger version for bigger gigs
Colossal wrote: ↑Thu Jan 04, 2024 11:51 pm
Smokebreak,
Did you stick to the original schematic? Have you measured voltages? I am especially interested in the cathodyne; how balanced or unbalanced it is.
For the most part yes, but that was 10 years ago! Certainly I kept the PI and power section the same, as well as the vibrato section....also note the massive dropper for the preamp B+ .
I added an extra preamp stage upfront accesible via it's own input jack, and at somepoint around 5 years ago I became obsessed with a certain National amp(Westwood?), that was also a Gretsch amp, and realized it was very close to this amp, so I tweaked it to those values. So I guess topography is the same, but tweaked values with an added stage ha.
I'll be glad to measure voltages and see exactly what I did once I get around to building it's big brother. Alnico speaker sounds killer with this circuit
Colossal wrote: ↑Thu Jan 04, 2024 11:51 pm
Smokebreak,
Did you stick to the original schematic? Have you measured voltages? I am especially interested in the cathodyne; how balanced or unbalanced it is.
For the most part yes, but that was 10 years ago! Certainly I kept the PI and power section the same, as well as the vibrato section....also note the massive dropper for the preamp B+ .
I added an extra preamp stage upfront accesible via it's own input jack, and at somepoint around 5 years ago I became obsessed with a certain National amp(Westwood?), that was also a Gretsch amp, and realized it was very close to this amp, so I tweaked it to those values. So I guess topography is the same, but tweaked values with an added stage ha.
I'll be glad to measure voltages and see exactly what I did once I get around to building it's big brother. Alnico speaker sounds killer with this circuit
Sounds like a fun amp! I have been investigating cathodynes of late and was curious about the 213's design. It's very simple with few parts. I have found some imbalance makes for a better overdriven tone.
Wow! Just wanted to comment on the obvious to help keep it in mind. A cathodyne (concertina, split-load, whatever) PI has no gain. So, whatever you are doing to the signal, it needs to be done before the PI. It is a really great choice for clean tone. Also, I used a cathodyne in front of a pair of 6SN7 outputs (yes, 4 triodes) because they didn't respond well (IMO) to either paraphase (a la Ampeg) or typical LTP (Fenderish.) I actually liked the result pushing the 6SN7's with the cathodyne. This PI clearly has it's place.
Smokebreak3 wrote: ↑Thu Jan 04, 2024 11:43 pm
Yea that tone control is neat, it acts as a mixture of cathode bypass on one side, and high frequency dump on the other, or a mix.
Not to go off topic, but that tone control looks similar to the Tone King Imperial "Mid-Bite" control. Different values, but same arrangement.
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Colossal wrote: ↑Thu Jan 04, 2024 11:51 pm
Smokebreak,
Did you stick to the original schematic? Have you measured voltages? I am especially interested in the cathodyne; how balanced or unbalanced it is.
I should clarify...I am interested in the lower part count, directly coupled cathodyne. I found a post from Gingertube on another forum stating that Kevin O'Connor uses a 15-22k grid stopper on the front end of a cathodyne, where Merlin lists 470k - 1M as his go-to values for preventing frequency doubling. Interestingly, another comment from Gingertube states that "tuning" a cathodyne to better handle overdrive conditions (when the cathodyne is being pushed into imbalance and starting to fall apart) can be done with 15-47k grid stoppers on the power tubes. We know this is generally OK to do without an appreciable loss of high end sparkle and presence due to low Miller capacitance. I've used 15k on Tweed Deluxes in the past with no ill effects to tone.
I have not seen any Magnatone 213 or related circuits where the schematics show the idle voltages for all stages and the power supply. I'd sure be interested to know what the operating points were for all stages in a 213.
Smokebreak3 wrote: ↑Wed Jan 03, 2024 10:07 pm
Anyways, I'm gonna do a 6L6 version, but without the trem, just a bare bones version of the core of the amp.
I have a Tremolux chassis that I am planning to stuff with some kind of Tweed-ish thing, sans the tremolo (I decided), but the stripped 213 idea fits well with that. I was thinking a 6k6 primary OT so I can run 6V6s, 6L6s, 5881s, or EL34s. It will run at pretty low voltages and be cathode biased at 250R. I have a pretty seriously modded 5E3 which runs like this and it is really good.
So, I answered my own questions by converting a modded 5E3 into a Magnatone 213 (sans the vibrato circuit). The as-built schematic looks pretty much like what Steve posted. I used 22nF coupling caps in the preamp, instead of 47n. The direct coupled cathodyne PI works well (hey, and less parts too). I used 22k to feed the grid from the preceding plate. Worked fine. I have a 10kB trimmer in series with the cathode resistor (left over from the previous amp) and found the sustain to be better and with more apparent depth with a greater imbalance. Great tone in the amp. Not as loud as its predecessor, maybe a little darker sounding, owing to the unbypassed cathodes throughout the preamp. Plenty of low end on tap and not flabby either. I may fool with adding some bypass caps on the first stages, just to give it a little more push. I like my clarity. The Tone circuit works well. No need for a master volume. I rolled preamp tubes and found something that works great with my 335; a balance of gain, sparkle, and clarity without too much pick and finger sensitivity. A 12AY7 in V1 doesn't have as much gain but sounds fantastic. Better balance of piano-like attack and a little better range on the Tone knob. The choice of tube in V2 can really affect the voice and onset of overdrive. Overdrive is very good.
