1939 guitar amp

[PRR]

Will somebody build this? DIY guitar amp from 1939.

http://www.clarisonus.com/Archives/Amp_Design/GA39.pdf

[bigsbybender]

I have plenty of 56's and 57's but no 45's.

Triode output looks like it may have a unique sound....  I guess Edcor could do up the interstage transformer. 30hy choke plus a field coil is clearly pre-war .  Not too different from some of these old Hammond Tone Cabinet amps I have, but this doesn't have choke input.

I wish I had all of the parts on hand, I'd try it.

[Willabe]

Will somebody build this? DIY guitar amp from 1939.

Why?

You must see something in this amp/build that is very promising, please tell us more.


        Thanks,     Brad      

[moonbird]

Looks cool -- really love the looks of these old tubes!! I might have a 45 or two to contribute. I am sure they would NOT match (LOL).

I have several interstage transformers -- but how the heck do you know which one you need? All I have is a VOM to measure DCR but that is about it. It would seem the interstage would have a huge effect on the sound of the amp -- how would you know if you got it right??

I will join the chorus. Why the interest in this amp??

[John]

Maybe because it is about the ONLY amp he's not worked on? 

[kagliostro]

Sorry for the naivety

what is a Speaker Field and how acts ??

Thanks

Kagliostro

[sluckey]

what is a Speaker Field and how acts ??

A "speaker field coil" is an electromagnet mounted on the speaker. It functions the same as our modern permanent magnet.

[kagliostro]

Again Thanks Sluckey

Kagliostro

[PRR]

> Why the interest in this amp??

1939.

Much older than most guitar amps.

> how the heck do you know which one you need?

Read the article. You savage a 1935 radio. Power and output stage nearly intact. Just add preamp where the tuned amplifiers were.

[moonbird]

Oops didn't see the PDF -- yes I have seen this one before.

So the bottom line on *my* interstages that I bought (cheap) -- is that no one knows how to use them. (if PRR can't help me WHO can??) Great!?! (LOL) Can't use them for radiation shielding in my bomb shelter anymore either I guess (dating myself). Oh well <grin> ...

Would you believe it -- I have one Peerless speaker motor for a single-coil homemade acoustic guitar pick-up (see article). Wow what an adventure that would be    (my wife might have me committed somewhere)

(FYI - I bought the Peerless speaker cab (just like the one in the picture) and put a 8-inch speaker in it for a harp amp - I read somewhere that I could reach harmonica nirvana -- but alas -- I am still earthbound <grin>)

I will look for the 45s -- no I don't have a 1939 radio ... still looks fun

[RicharD]

Why?
 

He's my taunting me.   

[terminalgs]

cool!

Hammond sells some interstage transformers:

http://www.hammondmfg.com/124.htm

the 124E has dual secondaries, so in parallel, flipped around you could have 34k/15kCT...  do those three gain stages have umph to let the signal drop like that?    the other 124's almost all 10k:90kCT..

The PT would be a trick, right?  aren't those old tubes all 2.5v heaters?   you could put a couple 56's in series to get 5V (tho your 80 is using that already),  but the 45's cant be serialized....

[RicharD]

All the tubes in this circuit are 2.5V.  The 56 is listed as having a Rp of 9k5 - 12k so I'm guessing the interstage transformer should have a Zin of about 50k.  There is a 1M resistor hanging off the secondary so running with the 10:1 rule, I'm guessing the secondary should be 100k CT tops.  I'd probably try a 50K 1:1 CT interstage transformer first.  The RCA cut sheet for the 45 lists a 5k load in self biased push pull.  I'd run and hide from the field coil speaker unless you got one hanging around you're just dieing to use.  The 80 rectifier tube doesn't look characteristically all that different from it's (dare I say) more modern counterparts.  The 56 is the bottle with the lowest DC rating (250V) so I'm guessing a B+ of 230 - 240V might be ideal.  The 57 is the predecessor to the 6J7 which precedes the 6SJ7.  That part should be pretty straight forward.

I'd love to tackle this project but I have none of the tubes, transformers, or sockets.  Certainly not within my budget these days.

[DummyLoad]

Why?
 

He's my taunting me.  

as well...  


EDIT: i don't have the tubes. nor can i locate more modern equivalents...
type 57 is very similar if not actually a 6J7
type 80 is close to 5Y3G
type 56 is close to ? 
type 45 is close to ?

--DL

[DummyLoad]

use 6BH7 for type 56 sub, 6J7 for type 57. for the 45... well a 45 (maybe sub 6BX7 or 6BL7?). we'll need ~~110Vpk at the grids to make 12W - yup AB2 - straight out of the datasheets. looks like interstage will need to be step-up around 1:2 or 7K to 15K plate Z (single plate to P-P grids).
i don't have any of the tubes or sockets for tubes listed in the schematic.  numbered tubes are becoming harder to find and my antique electronics collector won't sell me any due to fact he still needs repair stock. so unless someone here can point me/us to a supplier that won't terrorize the wallet, i'm out.   

stancor interstage - pg. 7

http://www.clarisonus.com/Archives/Trans/Stancor61.pdf

max bias is 10mA any of the interstage single plate to P-P gird they sold.

would the A-62-C work?

--DL

[Heinz]

Using a simple and inexpensive power transformer as a substitute for the interstage transformer might be a quick and dirty option. A transformer with a 230V primary and a double secondary with higher voltage (e.g. this one with 2x24V) should be close enough to make it work. To make it even dirtier you could use two 115V/24V transformers with the primaries in series and the secondaries coupled out of phase. These parts may already be in your junk pile.
The frequency response should be sufficient for this application, and it can always be replaced with a quality part once you win the lottery.

[terminalgs]

the 6.3v versions of the 56 and 57 are   the 76 and 77 tubes.   i have a 77 and some 80s.  a successor to the 45 was the 2A3,  which go for stupid money if NOS, Sino or sovtek new for $55/$80/pair.

here's more about the 45s and their successors the 2A3s:

http://www.single-ended.com/2A3/2A3single.htm

[moonbird]

The reading I have done says that the 6B4G is a 6v, octal, directly heated cathode version of the 2A3. If you go the Tubelab.com, he claims that some 6AV5G/GT tubes are very very close to 6B4's but indirectly heated. 6AV5G/GT are big TV tubes that are still a "dime a dozen".

6B4s used to be cheap but now go for over $50 each - even the cheapo Ruskie/Chinese ones.

PRR - were you interested specifically in a directly heated cathode tube for this amp?? If so, the coolest directly heated cathode guitar amp I have every seen on the web is here:

              http://www.ampbooks.com/home/amp-technology/battery-amp/

It uses old 3V and 1V battery powered radio tubes from about this same era. I was thinking about trying to use a small 12V dc boat battery as the power supply for one with the necessary voltage divider setup. These tubes are still pretty cheap - especially for goofing off. I would be too chicken to try over driving a 2A3 or even a 6b4.

[RicharD]

>You savage a 1935 radio.

That's really the only way this could possibly happen.  I perused fleaBay.  I found this somewhat likely candidate.  It's a hundred smackers, pickup only in Stevens Point, WI.  http://www.ebay.com/itm/Vintage-Sparton-Radio-/300590504589?pt=LH_DefaultDomain_0&hash=item45fc971a8d

We know a vintage radio guy here in central TX but he's gonna want a lot for anything from the 30's.

[DummyLoad]

alas! i've found you!  32 buks + ship.

http://www.ebay.com/itm/Universal-Interstage-Transformer-20000-ohm-MADE-USA-/110665341813?pt=LH_DefaultDomain_0&hash=item19c42b1b75#ht_921wt_1163

 

--DL

[PRR]

> somewhat likely candidate

Ugh, parlor radios are huge. I've walked away from two this year: one $60 (negotiable) at ReStore, and one on the side of the road in the rain for $20.

Yes, a few buyers are over-paying for junk, thinking they can flip them.

Certainly on parlor-tall models, the shipping eats all profit.

> he's gonna want a lot for anything from the 30's.

Talk. Most radio guys have stuff in the back, too ragged to sell. They hope to salvage parts..... in fact 90% of that treasure will go to their children and be scrapped at $0.02/pound. Most such guys would be sympathetic to a sensitive re-creation of a scrap-box project from that era. AND know what radios' audio sections/parts are a glut on the market because their RF/IF sections fail most often.

> i've found you!

Not truly "universal".

It will work for power grids which never go positive.

It will "work" in a pos-grid power section which is only played for "show", where getting FULL POWER is not essential.

The two-'45 output stage in that article must run POSitive-grid; '45 won't make much power negative-grid. The grids look like about 2K each, and pull a whopping 22mA peak. Since the '56 driver flows only 5mA, we need a considerable step-DOWN, like 4:1 from plate to one grid, and grid windings of low resistance.

An interesting power triode, much more available than the juicy and over-collected '45, is the 6N7 (similar: 6A6, 11A6, 53).

BTW: when looking-up 2-digit tubes on Frank's, try the syntax "^56$", "56$", or "^56$". As some of you will know, this is RE for start/end/both of match, so you don't get a ton of 4-digit tubes that happen to have "56" in the middle.

[DummyLoad]

It will work for power grids which never go positive.

well, we're screwed then...the only thing left, other than salvage, that'll stand that kind current and has those specs is 2A3/300b hi-fi stuff that goes for crazy $$$. we're talking hundreds for a chunk of copper, "specialty" iron, and varnish.

no thanks, i'm out. :-\

back to the 4E27A champ with a pentode driver. hopefully i'll be posting something in the next day or two. having trouble getting all the parts together - i misplaced some of the sockets. :(

"^56$", "56$", or "^56$"

^.*$   

--DL

[PRR]

> ...the only thing left, other than salvage

As per the original, I think the mojo is in the "salvage".

[RicharD]

Ahem....... Oh Peeeete!

[RicharD]

I have all the tubes but..... the 56's and 57's are actually 26's and 27's which appear to be 2 volt versions of the same tubes.  A friend brought over 2 boxes of tubes and a drug store tube tester that reeks of B & K.  He said, "take it all or it goes in the trash."  Nice to know I'm on par with the trash.  Not pictured is a pair of old Sylvania 6BQ5's with black plates.  Obviously used but gettering looks awesome.

[HotBluePlates]

So what you're saying is I shoulda asked if you had any 807's before I bought some... 

Treasure to me, but trash to the wife!

[PRR]

> appear to be 2 volt versions of the same tubes.

Check that.... '26 appears to be naked filament not heater-cathode.

Use-what-you-got is of course in order.

The '45 is slightly collectable.

[DummyLoad]

yas, u rang?

your iron or mine?  :-)

--DL

[RicharD]

I got a few 807's laying around.  Pity about the 26's.  It's a decent size box of old tubes.  Maybe there's something else we could use.  I was perusing the box when I remembered this thread.  Need to sit down with the box and have Frank's close at hand..... and a beer in the other. 

Just to completely digress, what about the 6EJ7/EF184?  That's the tube at first glance looks like an EF86.  I already have a pile of them with another handful added from this load.  Very linear looking curves.       

[tubeswell]

Why?
 

He's my taunting me.  

as well...  


EDIT: i don't have the tubes. nor can i locate more modern equivalents...
type 57 is very similar if not actually a 6J7
type 80 is close to 5Y3G
type 56 is close to ? 
type 45 is close to ?

--DL

FWIW says here http://www.r-type.org/exhib/aag0016.htm that the 56 is 'sensibly equivalent to a CV611'  (but trying find 'CV611' doesn't help much - sorry 'bout that) and here http://www.r-type.org/exhib/aaa1037.htm that the 45 is 'sensibly equivalent to a CV610' (same story there too).