Dearmond / Martin R-15 VS. 5E3

[worth]

I was taking another look at this amp that so many people are crazy about. The difference between this and a 5E3 seem to be .. the R-15 has a 12AX7 in V1, different pot values, .047 caps in the PI, and probably bigger transformers. It seems that the gain would be a bit over the top with a 12AX7 in V1. Would different pot values account for tonal difference ? I'm thinking if I had a 5E3 with a 12AX7 in V1 and huge transformers, it wouldn't be much different than the Dearmond.

[sluckey]

Yep, except for the tremolo.

[Willabe]

There's a thread here about, oh, maybe a year back or so that talked about this.

They are very similar to each other as far as the circuit goes.

The volume and tone pots were a different values, 1M for 5E3, 350K for the Martin. You saw the coupling caps, and 12AX7 instead of 12AY7. A little more gain from the 12AX7, maybe that's why or part of why the difference in the coupling cap values, to strip back out some of the gain/bass?

Tone Quest Magazine did a review of this amp and they loved it. So much so they even had Merc. Mag. clone the iron and were selling clones of the amp for a while. You can still buy the iron for it from Merc. Mag. They gave the PT extra current on the heaters so you could use 6L6's if you want.

They said the OT was larger than a 15/20w amp, but never said it's almost a dead copy of a 5E3.          

IIRC, consensus was if you want to build one, just use a bigger OT and use a 500K (?) pot with an R across it to make it act like a 350K pot. Dummy Load even listed the value for the R.


                          Brad        

[HotBluePlates]

The volume and tone pots were a different values, 1M for 5E3, 350K for the Martin. You saw the coupling caps, and 12AX7 instead of 12AY7. A little more gain from the 12AX7, maybe that's why or part of why the difference in the coupling cap values, to strip back out some of the gain/bass?

Tone Quest Magazine did a review of this amp and they loved it.

What's the one thing most people would change about the 5E3? Maybe reduce the mud under distortion? Bigger RC equals lower turnover frequency.

Pretend the 5E3's volume controls are full-up; ignore the output impedance of the previous stage (it counts, but will impact both situations about the same). 1M and 0.1uF -> RC= 0.1 -> 1/(2*Pi*R*C) = -3dB @ 1.6Hz (!?).

For the Martin/DeArmond, we have 350k and 0.01uF. 1/(2*Pi*R*C) = 45Hz. We still have full guitar range, but have likely lost some of the mud, just in the coupling between the first and second stages.

You noted the input 12AX7, but the reduction of the volume pots to 350k is a heavier load on the input stages, and reduces the actual gain of the input stage. Pretend the tone circuit doesn't exist; again, it will affect the DeArmond and 5E3 similarly.

The effective plate load under signal conditions is the actual plate resistor in parallel with the following stage's grid reference resistor (or volume control). With a 1M volume control or grid resistor, the 100k plate load looks like 100k ll 1M = 90.9k. With a 350k volume control, it looks like 100k ll 350k = 77.8k.

Let's assume the 12AX7 has a mu of 100 and an internal resistance of 60k (these exact values vary depending on the operating point). Gain with the 5E3 values is A = 100*[90.9k/(90.9k+60k)] = 60. With DeArmond values, the gain is A = 100*[77.8k/(77.8k+60k)] = 56. Not a whole lot of drop with the DeArmond values.

What about 5E3 with a 12AY7? Assume mu of 44 and internal resistance of 25k. A = 44*[90.9k/(90.9k+25k)] = 35. So with 5E3 values, swapping a 12AY7 for a 12AX7 nearly doubles the gain of the input stage (noticeable).

So the DeArmond keeps most of the hopped-up 5E3 flavor, but shaves the bass about 4 octaves at the input stage, and by an octave in the output stage. That oughta keep the sound more authoritative, better under distortion. If they used a bigger OT for less transformer saturation, then it might convincingly sound bigger with bigger/more speakers.

[Willabe]

Thanks for the in depth explanation HBP. It is very helpful to hear it explained like you did.


                       Brad     

[leonc]

Just finishing a build of the R15T with the MM transformers. If this build is any indicator, I'd say HBP's comments are right

Thanks for the in depth explanation HBP. It is very helpful to hear it explained like you did.


                       Brad     

on track. This has to be one of the best sounding amps I've had the pleasure of playing through! You get the harmonically rich 5E3 type sound with notably less squish. More clean headroom and generally more pleasing overdrive.

Btw, I'd hazzard a guess that the ot is built rather different from that of tb e 5E3.  Will post a photo of that soon as well.

[kagliostro]

This is incredible

I was looking just 1 minute ago to the schematic of the martin-112t amp

but not here or on Doug's database, on a completely different page on the web

then I returned to the forum and opened this old tread of 2012 that has received a new post

and what I see on the firs link on the first post .... the same amp schematic

This is really incredible

Franco

[tdvt]

Just finishing a build of the R15T with the MM transformers. If this build is any indicator, I'd say HBP's comments are right

Thanks for the in depth explanation HBP. It is very helpful to hear it explained like you did.


                       Brad     

on track. This has to be one of the best sounding amps I've had the pleasure of playing through! You get the harmonically rich 5E3 type sound with notably less squish. More clean headroom and generally more pleasing overdrive.

Btw, I'd hazzard a guess that the ot is built rather different from that of tb e 5E3.  Will post a photo of that soon as well.

I had never heard of these but doing a search, checked out your vids & saw your construction pics on the Guild forum.

I'd be interested in hearing specifics of your build, especially the trem (varistor).

Thanks,

TD




 

[tdvt]

Found this cool calculator to "create" odd-valued pots

http://www.diystompboxes.com/analogalchemy/emh/emh.html

Seems like it would be helpful in building this circuit.

TD

[kagliostro]

I think all people that would like to experiment with varistor vibrato must read with attention this thread

http://ampgarage.com/forum/viewtopic.php?t=23839&postdays=0&postorder=asc&start=0

there you can find the ultimate solution to the problem related with the varistor availability

Franco

[octal]

Tone Quest Magazine did a review of this amp and they loved it.
                          Brad       

The funny thing about this is that based on the schematic, it looks like the amp uses those "packaged electronic circuit" R-C combo things, which usually contain the nastiest low bid ceramic caps out there. I can only imagine how outraged those Tonequest writers would be about a new boutique amp which used ceramic caps! 

[Willabe]

The funny thing about this is that based on the schematic, it looks like the amp uses those "packaged electronic circuit" R-C combo things, which usually contain the nastiest low bid ceramic caps out there. I can only imagine how outraged those Tonequest writers would be about a new boutique amp which used ceramic caps! 

Not true. 

(Have you every read Tone Quest?)

Tone Quest Magazine did a review of this amp and they loved it. So much so they even had Merc. Mag. clone the iron and were selling clones of the amp for a while.

[birt]

I think all people that would like to experiment with varistor vibrato must read with attention this thread

http://ampgarage.com/forum/viewtopic.php?t=23839&postdays=0&postorder=asc&start=0

there you can find the ultimate solution to the problem related with the varistor availability

Franco

my electronics knowledge is limited but i'm just thinking out loud here:
varistors have less resistance as the voltage goes up, because the LFO changes the voltage the resistance of the varistor changes. this controls the vibrato effect right?
when i think about parts that have a smooth resistance change according to the voltage across them i tend to think of light bulbs. they do the opposite (resistance goes up with the voltage) but in my mind that's not a big issue. could small (12V, 24V,..) light bulbs in series or parallel be used with the LFO in that circuit? again, i'm just thinking out loud and might be very wrong.

[leonc]

I think all people that would like to experiment with varistor vibrato must read with attention this thread

http://ampgarage.com/forum/viewtopic.php?t=23839&postdays=0&postorder=asc&start=0

there you can find the ultimate solution to the problem related with the varistor availability

Franco

FWIW, I had 6 or 7 varistors left over from a Magnatone 213 clone that I built maybe 5 years ago. I bought a couple varistors from Gary Croutreau (Juke amps) who pretty much has the market cornered on the Workman brand varistors used in the original Magnatones. I used some of his in my 213 clone and the vibrato came out GREAT in that amp. Then I found a couple with similar specs from some web/electronics store for dirt cheap and bought them as well.


Well, seeing as I had these, and seeing as there are no specs for the varistor used in the R15T's oscillator (331-BNR-7), I figured I'd try all of my left-overs when I built my first R15 a couple years ago and see if just by chance, any of them were equivalent to the 331-BNR-7. I can tell you, none of them worked. It was just a lark...the varistor in the R15T oscillator presumably serves an entirely different purpose than those used to produce the warble in the Maggie's vibrato...

[tdvt]

I figured I'd try all of my left-overs when I built my first R15 a couple years ago and see if just by chance, any of them were equivalent to the 331-BNR-7. I can tell you, none of them worked. It was just a lark...the varistor in the R15T oscillator presumably serves an entirely different purpose than those used to produce the warble in the Maggie's vibrato...

So what did you use in the end?  P/N?

Also wondering if you figured out what the OT primary impedance is?

[kagliostro]

Here is the patent used by Magnatone

you can read a detailed explanation of the Magnatone Varistor Vibrato circuit

http://www.google.com.au/patents/US2988706?dq=2988706&ei=EmzBTtfzMIvRmAWH-6WtBA

Franco

[PRR]

> R-C combo things, which usually contain the nastiest low bid ceramic caps

In the day, you could specify what crap you wanted.

Yes, 99.44% went into $9.98 radios, and low-bid was seriously cheap.

However McIntosh used a R-C blob in both (same part) their last tube preamps and their early transistor preamps to set-up the RIAA equalization, where tight matching and no-crap sound were vital. Obviously they wrote a tight spec, discussed it with the blob maker, tested samples and production deliveries, and PAID for what they wanted.

Martin probably worked-with Centralab or A/B, though perhaps not to such a tight spec as McIntosh could afford to.

[leonc]

I figured I'd try all of my left-overs when I built my first R15 a couple years ago and see if just by chance, any of them were equivalent to the 331-BNR-7. I can tell you, none of them worked. It was just a lark...the varistor in the R15T oscillator presumably serves an entirely different purpose than those used to produce the warble in the Maggie's vibrato...

So what did you use in the end?  P/N?

Also wondering if you figured out what the OT primary impedance is?

As I mentioned further above, the work-around is very simple: don't use a varistor :)


Where Rowe used a 27K resistor leading to the varisotr, simply use a 68K resistor in it's place. This is how it's done in the little brother R5T model, which is damn near the same oscillator circuit.


As for the OT, yeah, the Mercury primary is 6.7K, so very close to 5E3, right? yes...but there's more to an OT than it's primary, secondary, turns-ratio...there's also construction, materials etc. The laminations of the core on the Merc are a little over 1.5" thick. Now I don't have an actual tweed Deluxe nearby to compare to...but I imagine that's considerably more iron. It's also quite a bit taller than what I recall of the 5E3 OT, it's 3" tall. So no, it's not a Bassman OT, heheh, but I suspect there's notably more to it than simply plopping in a 5E3 OT.


And my ears absolutely tell me that this amp lacks the flubby low-end and overly compressed squishiness of a 5E3. I built the same amp a few years ago with MC transformers (which I do really like)...but this version with the Mercuries sounds (and "feels") WAY better. It's got a much more mediate response (particularly on the normal channel with the larger coupling cap and smaller cathode resistor). It does start getting a bit more compressed with vol above 3:00 or so...but not nearly as much as my earlier version with the MC transformers. In the case of this amp, I'd say the much higher cost of the Mercuries is ABSOLUTELY worth it.

[octal]

The funny thing about this is that based on the schematic, it looks like the amp uses those "packaged electronic circuit" R-C combo things, which usually contain the nastiest low bid ceramic caps out there. I can only imagine how outraged those Tonequest writers would be about a new boutique amp which used ceramic caps! 

Not true. 

(Have you every read Tone Quest?)

Tone Quest Magazine did a review of this amp and they loved it. So much so they even had Merc. Mag. clone the iron and were selling clones of the amp for a while.

Sure, I've read ToneQuest. It's well written, but there seems to be a lot of emphasis on "vintage mojo" and cork sniffing. I get the impression that there's some "hearing with their eyes" that goes on with their writers. "The blue vintage Astron caps were woodier sounding than those harsh modern Orange drops etc. "  I could see their writers_maybe_ going for ceramic caps if they were what was originally in a vintage amp- for authenticity's sake.  Anyway, my comment was just intended as a throw-away quip about  component fetishes. As PRR has mentioned, even though most of those"packaged circuits" used low quality parts, evidently it was possible to spec better stuff.  It probably doesn't matter either way. 

[Willabe]

.........but there seems to be a lot of emphasis on "vintage mojo" and cork sniffing. I get the impression that there's some "hearing with their eyes" that goes on with their writers.

I own and have read every issue they've released. IMO, I think there's very little cork sniffing going on there and little 'hearing with their eyes'. (Other wise I would have stopped buying them long ago.) But nobodies perfect.   

They have had their hands on many vintage amps and played them for hours not a single afternoon. There is some mojo in some/many of the old amps that you won't hear in new clones for various reasons, some maybe known, some not.   

And, they have given very high praise to both new amp clones and new designs, built with eyelet/turret boards and built with PCB's many times over the years. 

As far as;

"The blue vintage Astron caps were woodier sounding than those harsh modern Orange drops etc."

I wanted to get to the bottom of if there's a difference in tone coupling caps myself. I think there definetly is at this point.

Have you read any of this thread;

http://el34world.com/Forum/index.php?topic=19534.0

[leonc]

Kinda drifting off topic, but one funny thing about caps, quality and tone... Anyone get to play through a great old Valco amp, like a 1690T, a 1624T (early version), a 1696TN, a 1688TN? They were chock full of cheap RMC ceramic disc caps, often in critical "tone" locations, like coupling caps. And yet, those are some of my favorite sounding amps of all time!!


Here's my 1688TN clone that I built with CT transformers and a number of ceramic disc caps, just like the original.


https://www.youtube.com/watch?v=CIwVKLR8mxs

[Willabe]

Kinda drifting off topic, but one funny thing about caps, quality and tone... Anyone get to play through a great old Valco amp, like a 1690T, a 1624T (early version), a 1696TN, a 1688TN? They were chock full of cheap RMC ceramic disc caps, often in critical "tone" locations, like coupling caps. And yet, those are some of my favorite sounding amps of all time!!

Their part of the tone. 

[tdvt]

As I mentioned further above, the work-around is very simple: don't use a varistor :)


Where Rowe used a 27K resistor leading to the varisotr, simply use a 68K resistor in it's place. This is how it's done in the little brother R5T model, which is damn near the same oscillator circuit.


As for the OT, yeah, the Mercury primary is 6.7K, so very close to 5E3, right? yes...but there's more to an OT than it's primary, secondary, turns-ratio...there's also construction, materials etc. The laminations of the core on the Merc are a little over 1.5" thick. Now I don't have an actual tweed Deluxe nearby to compare to...but I imagine that's considerably more iron. It's also quite a bit taller than what I recall of the 5E3 OT, it's 3" tall. So no, it's not a Bassman OT, heheh, but I suspect there's notably more to it than simply plopping in a 5E3 OT.


And my ears absolutely tell me that this amp lacks the flubby low-end and overly compressed squishiness of a 5E3. I built the same amp a few years ago with MC transformers (which I do really like)...but this version with the Mercuries sounds (and "feels") WAY better. It's got a much more mediate response (particularly on the normal channel with the larger coupling cap and smaller cathode resistor). It does start getting a bit more compressed with vol above 3:00 or so...but not nearly as much as my earlier version with the MC transformers. In the case of this amp, I'd say the much higher cost of the Mercuries is ABSOLUTELY worth it.

I had saved the R5T schematic but hadn't compared the two, they really are nearly identical, I wonder what the "varistor" offered to make it worth it?

Thanks for your insights on the OT/tone as well.

I had seen/heard your 1688TN in another thread, beautiful sounding amp!  You have chosen some nice projects.


TD

[leonc]

...
I had seen/heard your 1688TN in another thread, beautiful sounding amp!  You have chosen some nice projects.


TD

Thanks TD! Yeah, I go for the weirdies, LOL!


BTW...I tried puttering around with old stock pots last night. I got a hold of only one 650K pot and it turns out the pot is FUBAR...the material inside the pot must be messed up...it kind of cuts out at the end of the throw. But as long as I didn't set it wide open, it sounded pretty good. interestingly I tried a couple different 350K pots in the Normal channel and I have to say...something about them didn't work for me...can't quite put my finger on it...but the sound was just off a bit. Too bad because I "wanted" to like them. Anyways, that's just my experience/preference. I went back and put in the modern production CTS pot I originally had in there. (I had gone through all of my pots and found some that were notably less than 500K...I managed to find one 410K and one 424K so that's what I've got in there for the two vol controls.)

[tdvt]

Thanks TD! Yeah, I go for the weirdies, LOL!


BTW...I tried puttering around with old stock pots last night. I got a hold of only one 650K pot and it turns out the pot is FUBAR...the material inside the pot must be messed up...it kind of cuts out at the end of the throw. But as long as I didn't set it wide open, it sounded pretty good. interestingly I tried a couple different 350K pots in the Normal channel and I have to say...something about them didn't work for me...can't quite put my finger on it...but the sound was just off a bit. Too bad because I "wanted" to like them. Anyways, that's just my experience/preference. I went back and put in the modern production CTS pot I originally had in there. (I had gone through all of my pots and found some that were notably less than 500K...I managed to find one 410K and one 424K so that's what I've got in there for the two vol controls.)

Thinking I might try one of these before I continue my SE amp quest.

Did you stay with the DeArmond/Martin schematic, ie: Same B+ filtering, no screen resistors, no grid stoppers, etc.?

I have seen some recent posts about 40uf being on the edge for a 5Y3 for the first filter stage, but I suppose this was a proven production amp ....on the other hand better tubes back in the day....

Good thought on measuring actual pots looking for the low ones. I think I have one of the brown Fender 350K w/70k tap in the parts bin, is that what you tried?

[leonc]

Thinking I might try one of these before I continue my SE amp quest.

Did you stay with the DeArmond/Martin schematic, ie: Same B+ filtering, no screen resistors, no grid stoppers, etc.?

I have seen some recent posts about 40uf being on the edge for a 5Y3 for the first filter stage, but I suppose this was a proven production amp ....on the other hand better tubes back in the day....

Good thought on measuring actual pots looking for the low ones. I think I have one of the brown Fender 350K w/70k tap in the parts bin, is that what you tried?

Hey TV - I have made a couple tweaks, though not to the filter section. Yeah, I'm sure on the one hand that 40uF is pushing it. And on the other hand...these amps have been around for decades and I've heard no stories about them frying 5Y3s. I imagine if you stick with decent old stock 5E3s, it'll be okay. Some Brimars were actually rate at 32uF, IIRC...FWIW.


I have made a few tweaks to the circuit, minor stuff, just dialing it in to my taste. E.g., I knocked down the cathode-bypass on the trem channel to 5uF and I lowered the last to coupling caps from .05 to .03. Pretty minor in the scheme of things.


BTW, if you're on a SE amp search, you MUST find a way to try out a DeArmond R5 or R5T. I managed to get one a month ago and man, that is best damned single-ended amp I've ever heard, anywhere. For a SE amp, it's just unreal. With a good speaker (I've got a Rajun Cajun in there), it's just amazing how big it sounds. Here's a clip after switchin the speaker; bone stock beyond that.


https://www.youtube.com/watch?v=7nln38r3-nQ

[leonc]

And here are some shots of R15T build, now that the cab's finished.

[leonc]

And here's a shot of my R5T with his new big brother :D

[leonc]

Got a clip down yesterday.


https://www.youtube.com/watch?v=R25a4BCo5UI


Guitars are all plugged straight in. Dry signal panned right. Wee bit of delay panned left.

[tdvt]

Sounds great! & nice playing as always. Nice job on the cabinet too.

Since you mentioned it earlier (with the video), it got me thinking & I have been laying out an R5T. Without the trem, it's really close to a 5E2 Princeton, though I've laid out complete.

Seems like it might be a more manageable next project.

Keep them coming!

Best, TD

[leonc]

Thanks TD - first gig with it coming up this weekend...acid test!