1930's L.A. National dobro amp help needed

[tonealone]

Hello
I wonder if you can help me figure out anything about this amp. It has serial number 5781 and model number 6125AZ.
Is the cabinet original or was it made afterwords? The cabinet material looks the same as the early 30 amp, but have never seen one with compartments built into the top. Is the speaker original?
It has not been turned on for 20 years, so I won't.
Any info would be a great help.
Excuse the stupidity here, but how do I insert a photo to show you?

Thanks

[Michael Messer]

Hi Tonealone,

Welcome to our forum.

Without photos we cannot comment on your amp. To insert photos just click on ADD ATTACHMENT in the top right hand corner of a new post window. Do not use the Quick Reply window as it has no facilities for adding photos, changing fonts, posting videos etc...

Photos must be less than 1MB

Shine On
Michael.

[tonealone]

thanks for the photo help. Here is my amp...

[Michael Messer]

Hi tonealone,

I have seen similar National Dobro Corporation amps from the early/mid 30s, but not that model.

It is taller than the standard 6107A models, it has the two extra Dobro-style sound holes and it appears to have an opening top with hinges and those two rectangular panels at the back, which I have never seen before. Does the top open (?), if so it could be designed as a stand for a lap steel guitar. It also, with its components, looks more powerful than the 6107A .

Anyone have any ideas about this one?

Shine On
Michael

[tonealone]

Thanks for the info so far. Yes the top does flip up. here are some pics. I can't tell if it some custom work from many many decades ago, or if it is original. I can't find out any info on the model number, so I guess it's a mystery. So far anyways. Thanks a whole bunch

Attachments:

[Michael Messer]

Hi tonealone,

Seeing the photos in better detail; I am guessing here, but I don't think the box is factory built. It doesn't have the same handle, covering or corner protectors as other National Dobro amps of that or any period, and the speaker is not in the centre.

It is an interesting piece, but I do have serious doubts about it being factory made.

Shine On
Michael.

[tonealone]

Thanks for that Michael. I appreciate your feedback.

[mitchfit]

what tubes/valves are in it?

mitchfit

[Michael Messer]

They look to me like KT66 or KT88 tubes. (Known in the UK as 'milk bottles' ).

Shine On
Michael

[tonealone]

I just checked out the tubes. I've been afraid to pull them out, but I stared fear directly in the eyes tonight, and yanked them out. I've made a little sketch of what i found.  The tube that is shielded by the aluminum(?) cover, was unable to be removed, as it seems to be attached differently(?) than the rest.
Perhaps you guys will know about this. The 2A3's and the 5Z3 are labeled in the socket. The other two I gleaned the info off the tube itself. Looking at photo's of similar amps, I notice there is an extra tube in this model, #5 in my crude sketch (numbers inside the circles are my numbering system to keep track of the tubes)

[mitchfit]

closest i could come up with:

el34world.com/charts/Schematics/files/valco/national-dobro_6107.pdf

pre-valves would make your amp post 1939, [when that valve was originally released], although the actual 6N7 designation wasn't introduced 'til 1941. would guess the linked schematic was from pre '39 due to the 79 in V1 and 56 in V2.

[see 9/11/35 on linked schematic]

due to steadily rising prices from the audio-phyle hi-fi sector, would seriously suggest you score some more 2A3 output bottles soon, should the amp become a keeper.

www.ebay.com/bhp/2a3-tube

hope this helps,
mitchfit

[Deleted]

Ok here is my $0.02 worth, most likely made by Valco for National and these were good serviceable amps if you do decide to bring it up youself get or borrow a Variac and bring it to life slowly stopping at 117VAC if you are in the US or Canada, these were not designed to run on a 120-125VAC which most US electrical service has moved up to- Once you know the amp is stable you should not need a Variac to run it but the smart money says have a qualified amp tech go through it and save yourself the worry- there will undoubtedly be some things this amp needs and some of the originally spec'd parts will likely not be available- it is a beauty!

[billyclaire]

Definitely has a "home-made" look to some elements of it. The covering isn't as even as the factory would have installed nor is it a "correct" pattern. I'd guess someone adapted it to enable himself a more comfortable playing situation of some sort, whether he had a lap steel on top or something else. Also, that on-off switch doesn't look like something factory... cool amp nonetheless! I'd guess the tube in the can to be a 79 - maybe.

There's also the slot to the left looking at the back that's clearly to store something. Not sure what would fit... You don't suppose it could be for a movie projector? Storing the take-up reel there?

[Deleted]

Still must account for the model number stamped with the added Z... Likely a one-off custom order...

[timbercore]

I have one of these, same model # in a different cabinet. Seems to match the attached schematic, and while the case is different, the handle seems like a match to others online. Can't seem to add pics just yet.

Something I just noticed as the Variac warms it up is that the power transformer is marked as 25 cycles (with X stamped over 50 and 60) so my current theory is that this is a Canadian model, as my understanding is parts of Canada would have been on 25Hz utility power in the 30s. This could also explain the PM speaker (most other listings for similar models show field coil).

On mine, the rectifier tube had been broken by the super stiff power cord in shipping (total gamble from an estate sale in the western US). So I'd gotten as far as replacing it with 3-prong grounded, learning that the 3A plug fuse is not a common modern value, and bringing it up with solid-state rectification when I found this 25Hz hint.

Can't tell if that is stamped on OP's amp badge, however.