Distraction in the Form of a Thunderbolt

[HommeMarrBuckley]

Hello everyone,


I dunno why I have put this one off for so long--I sometimes have trouble motivating myself just to get that initial push.  My life has really got complicated this past year with family and work.  I have plenty of stuff to do but a lot of it isn't really enjoyable (work) so I found that I really needed to decompress.  A healthy distraction.  I have had nearly all the parts for probably two years now--it even has the head and speaker cab finished waiting.   This is one amp I never heard in person but have heard in recordings and has much praise. Really has piqued my interest.  The Supro 6420 (Solid State).


So, I want to start work on it.  Last part is coming soon (OT) and I have begun marking up a blank chassis.  I am using this schematic.
http://el34world.com/charts/Schematics/files/supro/Supro_Tbolt_6420_SS.pdf
But I need some help.
I would like to drill only once, or meaning do all the drilling and then no more.  I, unfortunately have had a moment or two where I thought I was done, started to install and then realized that, I forgot a mounting hole for the board or forgot a passthrough hole, etc.  Those aren't important as the face, so I need to consider 1 or 2 jacks.


I want the idea of having the single/parallel triode option on V1.  I don't how to implement this. I was wondering if someone could put that with 2 jacks (single/parallel) in layout format, OR if easier a layout with one jack and a SPST (single/parallel) that accomplishes same thing.  I like the idea of one jack with the single/parallel switch better because that will be so much easier to utilize while playing.
Warning: will be immensely appreciated but will most likely lead to more questions.


2) Shouldn't I have a 1meg resistor on the jack?  Almost every schematic I have seen, has this, but then again they also have 47k resistors here compared to 68k.


3) If someone could highlight on the schematic the PI section.  I know it's on V2 but where it starts and ends.


I will post pics as I go.  Just not really much to show right now. 
I will post my layout of components most likely next.  But figured, to get this answered so I can plan to start drilling.  I finish my builds but they sometimes take longer, this will be my 4th.


Thank you.

[tubenit]

The Supro 6420 (Solid State).

http://el34world.com/charts/Schematics/files/supro/Supro_Thunderbolt.pdf

I am thinking the SS stands for something other then solid state unless it's referring to the rectifier in the amp?

There has been info on the internet that Jimmy Page played one, but an interview with Jimmy Page stated he didn't use one?   

Since you haven't played one in person or heard one in person, have you listened to the YouTubes of the Thunderbolt?  I am thinking some of the other Supros are more well liked and that the Thunderbolt has some pretty mixed reviews?  I think you should build whatever you would like, so I am not trying to talk you out of it.  Just wondering if you've listened to YouTubes of them?

With respect, Tubenit

[HommeMarrBuckley]

I understand what you mean.
Yes, I have seen some videos and that is what sparked things initially.  I will look at things for a long time before I decide to go ahead.  Just to give you an idea, I already know, if I continue to try to build amps, what the next two I will have a go at.  But looking at this one right now.

The Supro 6420 (Solid State).

I am thinking the SS stands for something other then solid state unless it's referring to the rectifier in the amp?

Yes, the other schematic is marked TR for the tube rectified version.

[sluckey]

Copy the V1 circuit from the Marshall 1974 18 watt amp...

     http://sluckeyamps.com/18w/18w.pdf

[HommeMarrBuckley]

I was thumbing through my amp notebook and saw this from another schematic/layout

In terms of one jack and SPST switch.


Would this work for single/parallel switching? 
Having a switch like this--think it will induce popping?

[sluckey]

That wont work. Pin 7 is grounded all the time. And when you close the switch pin 2 will be grounded too.

[HotBluePlates]

... This is one amp I never heard in person but have heard in recordings and has much praise. Really has piqued my interest.  The Supro 6420 (Solid State). ...

... have you listened to the YouTubes of the Thunderbolt?  I am thinking some of the other Supros are more well liked and that the Thunderbolt has some pretty mixed reviews?  ...

I once owned a Thunderbolt back in the late-90's, then sold it.  I kind of regretted that, as it had a quirky sound that wasn't quite like anything else.  Two months ago, another Thunderbolt popped up for sale near me in too good a condition to pass up.  Tube rectified version vs your solid state.

The below videos capture the sound pretty well.  That said, compared to my Thunderbolt, Johan sounds like he has the Tone control turned way down (which is fine).  My amp is somewhat brighter.

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Word of warning:  These amps are a 2-trick pony.  You can play quiet cleans.  But to get the distorted sound you're hearing in the videos, you gotta be LOUD.  When I went to look at the amp I bought, we were playing it an an airplane hangar.  Had the volume up ~3/4, and was playing it next to the owner's newly-acquired tweed Bassman (also cranked pretty high).  The 15" speaker can be beamy, and the true sound of the amp isn't really heard when you're standing next to it but 20ft or more away where the audience would be sitting.  That seemed to be the point where the beamy sound mixed with the room sound.

Point of the above is if you can't crank it, the amp may not seem that exciting.

3) If someone could highlight on the schematic the PI section.  I know it's on V2 but where it starts and ends. ...

The phase inverter is a paraphase inverter.  It starts at the Tone control wiper.  See it as a gain stage (V2A) to one output tube grid, and a voltage divider (270k/12k) into another gain stage (V2B) to the other output tube grid.  Marked schematic attached.

[HommeMarrBuckley]

Thank you very much HBP for your post. 
I never saw that amp by amp comparison.  There is just something a tad darker and grittier to me with the Supro which is what sparked my interest.

Word of warning:  These amps are a 2-trick pony.  You can play quiet cleans.  But to get the distorted sound you're hearing in the videos, you gotta be LOUD. 
Point of the above is if you can't crank it, the amp may not seem that exciting.

Uh oh, another neighbor oppressor.  That seems to be only drawback.  Perhaps the addition of Vol, Tone, Master.  I won't consider that now because I can hear somewhere "just build it first" so that's what I will do.

The phase inverter is a paraphase inverter.  It starts at the Volume control wiper. See it as a gain stage (V2A) to one output tube grid, and a voltage divider (270k/12k) into another gain stage (V2B) to the other output tube grid.  Marked schematic attached.

Thanks, I was looking for sorting grounds.  2k2, 35uf, 12k, 3k9 and 470k resistor will be grounded with the B's (2 270Ks)  to the PI cap.

[Tony Bones]

I have made amps with paraphase inverters and enjoyed them. They sound different than concertinas (i.e. 5E3) which sounds different from longtails (i.e. 5F6) but they all sound good both clean and overdriven.

The tone control is the same as the Big Muff circuit in http://www.duncanamps.com/tsc/.  I have not ever tried it in a guitar amp (as far as I know) but it seems intriguing.

To add to what HBP said about the paraphase phase inverter, the way I look at it V2a drives the top 6L6 (V3) directly as though single ended. V2b takes a sample of the output of V2a and amplifies it to drive the other 6L6 (V4). It's inverted because that's what common cathode stages do.  The two drive signals end up at the same level, even though V2b is amplifer, because V2b starts with only a fraction of the signal from V2a. That''s what the 270k/12k voltage divider is for. It takes the drive to V3 and reduces it by 1/23.5. Then V2b amplifies it by a factor of about 23.5 (hopefully) so that both 6L6's get the same level.

From a strictly engineering point of view there are other ways to do the phase inversion that result in better balance. But I say it doesn't matter; if it sounds good then it is good.

So I'd build - in fact maybe I will build up the circuit soon - but I get the impression that amp building is a different activity for HMB than me.

[HotBluePlates]

... It takes the drive to V3 and reduces it by 1/23.5. Then V2b amplifies it by a factor of about 23.5 (hopefully) so that both 6L6's get the same level.

From a strictly engineering point of view there are other ways to do the phase inversion that result in better balance. ...

I suspect if we measured (or even worked faithfully at calculating), the gain for V2B would not equal the voltage division ahead of its grid.

I think that's a good thing in this amp, and a factor in why I bought it (again).  I didn't have any other paraphase amps hanging around.  And I've always noticed an interesting sound to them, presumably due to the little bit of imbalance in the output section.

[Ed_Chambley]

... This is one amp I never heard in person but have heard in recordings and has much praise. Really has piqued my interest.  The Supro 6420 (Solid State). ...

... have you listened to the YouTubes of the Thunderbolt?  I am thinking some of the other Supros are more well liked and that the Thunderbolt has some pretty mixed reviews?  ...

I once owned a Thunderbolt back in the late-90's, then sold it.  I kind of regretted that, as it had a quirky sound that wasn't quite like anything else.  Two months ago, another Thunderbolt popped up for sale near me in too good a condition to pass up.  Tube rectified version vs your solid state.

The below videos capture the sound pretty well.  That said, compared to my Thunderbolt, Johan sounds like he has the Tone control turned way down (which is fine).  My amp is somewhat brighter.

! No longer available
! No longer available

Word of warning:  These amps are a 2-trick pony.  You can play quiet cleans.  But to get the distorted sound you're hearing in the videos, you gotta be LOUD.  When I went to look at the amp I bought, we were playing it an an airplane hangar.  Had the volume up ~3/4, and was playing it next to the owner's newly-acquired tweed Bassman (also cranked pretty high).  The 15" speaker can be beamy, and the true sound of the amp isn't really heard when you're standing next to it but 20ft or more away where the audience would be sitting.  That seemed to be the point where the beamy sound mixed with the room sound.

Point of the above is if you can't crank it, the amp may not seem that exciting.

3) If someone could highlight on the schematic the PI section.  I know it's on V2 but where it starts and ends. ...

The phase inverter is a paraphase inverter.  It starts at the Tone control wiper.  See it as a gain stage (V2A) to one output tube grid, and a voltage divider (270k/12k) into another gain stage (V2B) to the other output tube grid.  Marked schematic attached.

Do you know the reflected impedance of the ot?
I have one I believe to be from this amp. It is 5. 9k / 8 ohms. Can you verify?


BTW, this one looks very nice. You have picked up a few nice different amps lately. Are you becoming a collector? BTW, I did sell my 65 twin and 65 deluxe reverb. Same person. What do you think of future price increases.? 

[DummyLoad]

a loooong time ago, (2007-ish?) richard and i built a clone of the thunderbolt on his breadboard. it is an intriguing amp no doubt about that, however, we both came the same conclusion, that while overdriven it had a lot of charm, setting up to play clean that was appealing though it was a challenge. we both agreed that it is/was pretty much a one-trick pony, so to speak, and we did not take it past the experimentation stage. this is also the time where richard came to the conclusion that the paraphase of the schematic that was floating around in cyberspace at the time was drawn incorrectly.

we were testing with vintage OT/PT salvaged from a PA that i can't remember and 6.6k:8 edcor GSXE OT. from what i've heard and seen so far, the common thing seems to be to play a thunderbolt mostly only overdriven may substantiate our finding. lastly, i do recall that the edcor had the best tone of the two, surprisingly enough.


good luck with your build, hopefully it will help fulfill your tone quest...     



--pete

[HotBluePlates]

Do you know the reflected impedance of the ot?
I have one I believe to be from this amp. It is 5. 9k / 8 ohms. Can you verify? ...

Sorry, just seeing this request.  I'll try to verify for you, possibly will take until next weekend.

BTW, this one looks very nice. You have picked up a few nice different amps lately. Are you becoming a collector? BTW, I did sell my 65 twin and 65 deluxe reverb. Same person. What do you think of future price increases.?

Maybe buying a few amps was my mid-life crisis.  I'm done with all that for the foreseeable future.  Beyond the foreseeable future, who knows?

I actually wonder if some of this stuff won't have prices drop (e.g., collectors pass away increasing supply and/or decreasing direct nostalgia), but no way I can predict the byproduct of the emotional attachments people have with these things.

[SILVERGUN]

Did you guys see this?:
http://www.classictone.net/40-18061.html

5K primary

[DummyLoad]

Did you guys see this?:
http://www.classictone.net/40-18061.html

5K primary

cool. they sell the PT as well. no need to buy MM. 


http://www.classictone.net/40-18060.html


--pete

[tubenit]

Have you heard Leon C.'s  Supro 1688TN?   This is probably my favorite YouTube "amp tone" video out there.  I hope to build this someday.

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http://el34world.com/Forum/index.php?topic=16657.msg164853#msg164853

He talks about building his 1688TN clone here: 
https://www.thegearpage.net/board/index.php?threads/new-build-supro-1688tn-video-added-in-post-32.1245510/

My understanding is the Gretsch 6159 has some similarites to the Supro 1688TN?

You might compare the Thunderbolt to the Gretsch 6159 (if you like the tone of Leon's 1688TN).

With respect, Tubenit

[HommeMarrBuckley]

Did you guys see this?:
http://www.classictone.net/40-18061.html

5K primary

Yea, A while back I put a lot of stock in the site where I found the schematic.  I noticed that some others used it.  Plus, on the schematic it notes others that chimed in on the development and I am assuming they had the original and opened it up.  If you google angelfire, bean's amps and supro 6420 you'll see open shots and a bunch of info--the site.  (The cap section mentions one being 20uF in some models and 30 uF in others--not sure what I did here--I have a bag of all the parts--not sure if I chose one or ordered both)  With the transformers, I went with what was suggested.  Another builder used different--a multiple impedance OT.   I chose to keep it stock from this besides trying out Steve's layout of the single-parallel inputs.  If getting to the grit - volume levels are an issue (HBP), I might ask about a master, but that will be down the road.
Ive had the Heyboer PT for months now and yesterday the Classictone OT arrived.  I should be pretty much good to go. 


Does this layout look ok?  Ignore any pencil/pen marks, how the physical parts are aligned that's what I was thinking to drill.

[sluckey]

I would rotate one of the transformers 90°.

[HommeMarrBuckley]

I would rotate one of the transformers 90°.

Gosh, feeling silly.  Was in rush and didn't even look at the bells.
I'll adjust the OT so classictone logo will read horizontal.
Well, that's why you post.

[SoundmasterG]

Its nice to see people still building these clones after I and several others helped Sean Weatherford get a readable schematic together. The data that I gave Sean was based on three original amps, one a tube rectified model, and two were solid state models. The Heyboer power transformer clone was made originally due to one of the solid state amps of the owner blowing a power transformer, and he had it cloned and ordered five transformers. I got one of them as part of the repair of the amps though I still haven't built my clone yet though I have all of the needed parts.


You may experiment with the coupling caps....the originals used ceramic caps and they provide a bit of grit to the sound that is unique to them. Get the best quality ones you can though as some ceramic cap types are lousy. In addition to trying a switchable parallel stage at the input, you can also use the un-used gain stage as an additional gain stage after the input stage, but I would just suggest if you do this to keep the gain of that stage on the low side or the amp will oscillate.


They are kind of a one trick pony, but they do sound cool and it is useful to have that sound in your arsenal. They aren't all that loud too if you are using a speaker close to the original Jensen. At least in comparison to a 5F6A or an AC30 or something. I prefer the Thunderbolt with four 10's myself but your mileage may vary.

Cheers!

Greg

[DummyLoad]

IF you must use ceramic caps for audio, use NPO or COG types. 1) ceramic caps are extremely microphonic. avoid them. 2) they are nearly as expensive as film caps in the voltage ratings and values we use. 3) leaded/thru hole production is being scaled back in favor of SMT and MLCC types. 4) class 2 ceramics (Z5U etc..) are piezoelectric, in that they generate voltage under vibration (combo amp) - much like a piezo mic/transducer - avoid them.
 
--pete

[HommeMarrBuckley]

Copy the V1 circuit from the Marshall 1974 18 watt amp...

     http://sluckeyamps.com/18w/18w.pdf

Steve, am I able to use switchcraft jacks with this single/parallel hi/lo inputs on your diagram?
or do I have to use Cliff?

[sluckey]

Either type jack will work just fine.

[HommeMarrBuckley]

Alright,
Looking at the schematic
http://el34world.com/charts/Schematics/files/supro/Supro_Tbolt_6420_SS.pdf
Im trying to go about this correctly.
This is first time Im building without a layout so using the schematic with lots of pictures.
So 12AX7
Pin 2 is grid triode B
pin 7 is grid triode A


Im looking off the schematic at V2A
The tone pot (500K) middle lug should connect to pin 7
Correct?


Or maybe it doesn't matter, could be pin 2 or 7
Im thinking it does.
I dont know much but I am using a bunch of pictures from two people that built it off this schematic
however, I just noticed that they reversed their pin order here with the second 12AX7 (one has it one way while the other is opposite)
Thanks


Edit:  I just looked off the original.  It should be pin 7--to middle lug of tone pot
So, what would the amp sound like if they reversed the order here?  Wiring pins 1,2,3 as 6,7,8

[sluckey]

There are two triodes in that tube. It doesn't matter which triode you call A or B. Pins 1,2,3 make up one triode. Call it whatever you want. Pins 6,7,8 make up the other triode. Call that whatever you want. Just don't go mixin' pins up!

I generally like to call pins 1,2,3 side A and pins 6,7,8 side B. But it doesn't matter. Sometimes the layout will dictate which pins you use for which triode.