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Post subject: 1951 National 1610 by Valco
Posted: Fri Feb 10, 2017 11:04 am
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Trying to sort this out from the other thread. Apologies for not being able to preserve posters original forum data(date/time/format/etc.)
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I won a bid on ebay yesterday so I will be back to tinkering at months end.
Posted a pic of the non-Fender in the lounge under new gear purchase thread.viewtopic.php?f=2&t=99747&start=495
I believe its a National version of the 1948 Supro made by Valco.

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Be very interested in that Valco amp. Esp, restoration process. I just missed out on a 1936 Gibson EH-150 amp, on EBay. Things are getting more and more $$$ these days.

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I got lucky w/ a min bid and no body bidding against me.
What I've been able to pick up since that post is that it was made in 1951, the ref to the 1948 Supro is the closest schematic I could find. I still don't know the model, but its not a "Chicago 51" and it appears to have a mod done already. Someone added a control to the top of the cabinet behind the handle, probably a volume or tone control. Unfortunately the leather handle is also missing but the hardware is there. It looks to be in otherwise very good shape. I should have it around the 26th.

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Very cool, I am looking forward to pictures and the go through
Good luck mud

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Post some pics of the little beastie once it arrives.Arjay

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To my surprise it arrived today, wasn't supposed to be here until Wednesday.
No pics yet, gotta get a full charge on the battery. A little later for sure though.

From what I can tell from just an external inspection, its in very good condition.
The tubes are all date matched RCA 0-35 and I'll assume they are original. The sockets are tube specific marked.
The serial number is X7xx and dates it to 1951.
The chassis is relatively clean and paint covered w/ a few small chips.
The output transformer is riveted to the speaker.
All the fasteners appear original.
The cabinet is in remarkably good condition, no water stains. Minor warping likely caused by heat(one rubber foot glide doesn't make contact)
The spare fuse packet and fuse is present but paper is torn/brittle. The 2amp fuse is undamaged.
The extra control pot is still a little confusing to me and has a .1uf-500v cap in series w/ the middle tab of the pot. The pot from what I can see has 4 tabs?, can't read any markings yet.
Original 2 prong Belton power cord.
Discoloration of the Tolex is most likely from cigarette smoke, small scuffs here and there, aged smooth texture.
Weighs approximately 13lbs. my scale max is 11,doh.
13 1/4" wide, 13" tall, 7" deep
Haven't opened the chassis yet.

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Here are a few pics:
Image
Image
Image
Image
Image

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Got it cleaned up a bit and prepped for a new 3 prong.
Took parts inventory and will measure resistor values, install new power cord, order new electrolytics on Wed.

Anybody have ideas on what the mod pot is? Tone control, I'm thinking.
What is the fourth lug on that pot?

Thanks

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That was my initial thought as well, given that it's wired in conjunction with that axial cap to create an adjustable RC network.
Arjay

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Finally found the model, National Comet 1610 and the actual schematic#(510-6) Dtd 1947. The schematic is nearly identical to the Supro Comet Dtd 1948. I'll post a link later.
http://www.valcoamp.com/download/valco_ ... 0_1625.pdf

Removed the death cap
Installed 3 prong
Tested all the resistors- 1 out of spec (20% over) 1 near out of spec
Ordered electrolytic's and replacement resistors

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What is the fourth lug on that pot? "It's a center tap"

Well it turns out that the pot is configured to operate at 1Meg using the three standard lugs or by using the fourth lug(opposite side) it operates at 500K. Never seen one of these before.
I'm going to leave this in place but out of the circuit for the first fire.

Also got the replacement handle ordered yesterday and the original hardware off.
Whatever jig/tool they used to separate and bend the tangs on those old handle clasps sure is impressive workmanship and surely designed to never be removed. Much leverage required.

Anybody familiar with Philmore output trannies?
I picked up a 4ohm universal replacement model on ebay, NOS w/ original box and wiring instructions. The size seemed right for a Champ style amp.

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sfceric64 wrote:

Anybody familiar with Philmore output trannies?
I picked up a 4ohm universal replacement model on ebay, NOS w/ original box and wiring instructions. The size seemed right for a Champ style amp.


A more critical spec is the primary impedance -- a pair of 6V6GT's typically measure around 8KΩ plate-to-plate in class AB operation. Arjay

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Looks like amp may have output stage in Class "A" push-pull. Impedance maybe lower for those 6V6GT. Closer to 5-6k-ohms. Prolly not important.

Idle bias dissipation will be much higher than Class AB. Around 70-75% of 6V6GT rated max.

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BMW2002Ti wrote:

Looks like amp may have output stage in Class "A" push-pull. Impedance maybe lower for those 6V6GT. Closer to 5-6k-ohms. Prolly not important.

Idle bias dissipation will be much higher than Class AB. Around 70-75% of 6V6GT rated max.


Good call, Steve. I should've examined that schematic more closely

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Both are right on as usual, that's why I picked up the O/T. Its spec sheet shows wiring for class A@5k, AB@10k and Parallel@2.5k w/ 6v6.
I don't think there is a problem w/ the original, but thought it'd make a good spare to have around.

Supposedly this amp operates like the Champ, w/ a little more frequency range/kick from the 2nd 6v6.

I should have the new electrolytic/resistors next week. Went w/ F&T's 30/10/10@500 and Sprague 25x25.
The resistors that are outta spec will be replaced w/ C-film or CC and there W rate doubled.

Any opinion/issues on amps w/o a chassis soldered ground?
This uses a solid wire from the Elec. Caps to each tube socket/pot/component connection. Seems ok as I measured for continuity and ohm's to everything as I did with the Deluxe. The C/T's from the power tranny included and my ground from the 3 prong are soldered to the sockets ground tabs.

Also, I was thinking of just snipping the leads from the old twist-lock caps and covering the exposed surface w/ epoxy to preserve and protect the chassis. The original primary cap has a visible small leak at the lead.

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sfceric64 wrote:

I don't think there is a problem w/ the original, but thought it'd make a good spare to have around.


A wise decision. Like stocking up on a few critical parts for a vintage firearm (like an M-1 Garand or a 1911 pistol). Arjay

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Very nice amp!
One suggestion... check those (I'd actually replace) wax covered paper coupling capacitors. Nearly every one of these that are over a few decades old leak DC voltage. I'd use Red Vintage "Astron" caps made by Jupiter. These maintain the vintage tone.
This will also save any precious NOS tubes you may choose to use.
http://www.partsconnexion.com/capacitor ... stron.html

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Thanks, I got lucky for sure on this one.
I'm gonna check for leaks and decide then. They look perfectly new, not a single bubble anywhere and no wax in the chassis.
I've got an alternate set of tubes for startup/testing, definitely don't wanna risk any of the date matched set.

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Don't be fooled by the external looks of the caps. Waxed paper capacitors went out-of-common use for a reason.
https://antiqueradio.org/recap.htm

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BMW2002Ti wrote:

Don't be fooled by the external looks of the caps. Waxed paper capacitors went out-of-common use for a reason.

https://antiqueradio.org/recap.htm


+1

They don't fare well where high ambient heat is common.
Arjay

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I will most likely replace them w/ Mallory 150's but I really want to hear the wax paper 1st to get a good tone comparison, as long as they aren't leaking DC.
Not looking to bust my budget anywhere on this one. The Red Jupiter's are a pretty close match to the tweed era tone.
Got the new F&T caps and the handle yesterday, waiting for the resistors.
Need to go by Lowe's and pick up the 9/64 nuts & bolts for the handle re-assembly.

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sfceric64 wrote:

Need to go by Lowe's and pick up the 9/64 nuts & bolts for the handle re-assembly.

Lowe's is going to sell you a pack when you only need a couple. If there's a mom & pop hardware store in your area, they will most likely sell you the 2 you need, for way cheaper. Happy hunting. :wink:

Quote:
sfceric64 wrote:

I will most likely replace them w/ Mallory 150's but I really want to hear the wax paper 1st to get a good tone comparison, as long as they aren't leaking DC.

Not looking to bust my budget anywhere on this one. The Red Jupiter's are a pretty close match to the tweed era tone.


IME, Mallory 150 are closer to later BF era tone. I'd stick with a good PIO (like Russian K40Y-9) or polypropylene ones designed for vintage tone. Jensen (Denmark) make some nice PIO caps. But, are even more $$$ than Jupiter Reds. For budget minded, nothing beats the Sprague SBE 600VDC 716P.

Those wax paper caps maybe leaky and give a tone to the amp that has a lot of distortion by overloading the signal grid with DC. It'll hard to match that tone.

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I'd go with Jupiter Reds or Yellows. Both deliver a nice creamy tone.
Arjay

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Quote:

Mallory 150 are closer to later BF era tone
Nothing wrong with that tone.

This is gonna be my experimental amp, its a fairly simple circuit. I plan on playing with it, a lot once I ensure it runs smoothly.
I've got .o22/.033/.047 in 716P, 150's, SoZo yel&blu and some generic oil caps to play with.

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Those will definitely get you some blackface tones. Arjay

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Having some issues w/ my right arm, kinda hard to get to this project one handed. I have all the parts/pieces I think I might need, maybe by next week I'll get my right hand back. The only new work I've done is, I added epoxy over the old cap can fiber for prevention/protection and to seal them. Removed the protruding connector ends 1st but kept the grounding lugs of each can.

Question: Any issue w/ replacement electrolytic orientation, maybe 45 degrees as there is not enough room
to lay them horizontal to the chassis?


Quote:

Lowe's is going to sell you a pack when you only need a couple
mom/pop joints are really scarce these days. I found what I needed at Lowe's, cost me $2.50 for an 8 pack of 3/16" x 3/4" nuts/bolts and a bag of #6 washers and now I have a set of 4 for the next time I need something this small.

Oh yeah trying to keep the tax man happy as well; should have that wrapped up this weekend.

Quote:
For this new amp project you should start a new thread.

:idea: Arjay


Last edited by sfceric64 on Mon Jul 10, 2017 9:58 pm, edited 1 time in total.

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Post subject: Re: 1951 National 1610 by Valco
Posted: Fri Feb 10, 2017 1:53 pm
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I have been following the other post so I am going to continue your new and improved 1951 National 1610 by Valco post
mud


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Post subject: Re: 1951 National 1610 by Valco
Posted: Tue Feb 14, 2017 11:05 pm
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Appreciate the support Mud, I've got use of my hand back and will start back at it Wednesday. I did attach the new handle and put together a cradle for the chassis today(this chassis needs one as its a Z shape instead of a Fender 3 sided shape, needs clearance for the tubes while allowing access to the sockets).


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Post subject: Re: 1951 National 1610 by Valco
Posted: Tue Feb 14, 2017 11:25 pm
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Glad you got use of your hands back. :)
The "z-shaped" sheet metal chassis is very similar to the early woody era Fender amps.

Image


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Post subject: Re: 1951 National 1610 by Valco
Posted: Wed Feb 15, 2017 12:36 pm
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In that picture, the 600 looks like it has lots of room compared to the National at just 4.5" from the front. Leo obviously gave plenty of consideration to topology and the repair techs' ease of access for repair.

I'm slowly doing some parts swaps, the folks that put these components in must have intended them to be permanent fixtures. I'm sure they didn't consider someone like me 60 odd years later replacing original parts.

I'll put up a couple pics later when finished with the soldering for the day.


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Post subject: Re: 1951 National 1610 by Valco
Posted: Wed Feb 15, 2017 4:37 pm
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A few pics of the repairs so far.
Image
Image
A look from the back, ready to fire it up later tonight or Thursday for initial electrical checks
Installed 3way plug, replaced the 8.2k that joins the 6v6's and removed the death cap
Image


Last edited by sfceric64 on Mon Jul 10, 2017 10:03 pm, edited 1 time in total.

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Post subject: Re: 1951 National 1610 by Valco
Posted: Wed Feb 15, 2017 4:54 pm
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Nice job rebuilding that power rail.

I'm putting you in for an ARCOM.

8)

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1951 National 1610 by Valco
Posted: Wed Feb 15, 2017 5:53 pm
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Thanks Arjay.
There's was really no where to go but up; the blue tape represents the L/R limits. The topology of this amp is way outta whack. I will most likely but hopefully not have to re-run the double 6.3v lines(undressed next to the plate/screen power & tranny). Thinking about maybe an indicator lamp in place of the tone mod if it doesn't work well or just patching it up after testing.


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Post subject: Re: 1951 National 1610 by Valco
Posted: Wed Feb 15, 2017 6:31 pm
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If you have to redo those heater lines, be sure to twist the pair uniformly between the sockets (just as you've seen in the old Fender amps). That should help minimize the ambient AC noise

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1951 National 1610 by Valco
Posted: Wed Feb 15, 2017 7:31 pm
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Retroverbial wrote:
If you have to redo those heater lines, be sure to twist the pair uniformly between the sockets (just as you've seen in the old Fender amps). That should help minimize the ambient AC noise

Arjay


Also, lift the grounded green line. Looks like it soldered to one of the socket metal rings.

I can't tell if the heater lines have a center tap. If not, you could add two 100-ohm resistors to each end of the twisted pair --- to make an artificial CT. This will also help to reduce the AC heater line hum.

Good job! Should sound much better, after the mods. And more reliable. :mrgreen:


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Post subject: Re: 1951 National 1610 by Valco
Posted: Wed Feb 15, 2017 11:30 pm
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Quote:
Also, lift the grounded green line. Looks like it soldered to one of the socket metal rings.

The heater line does have a CT and its sent to ground @ one of the rectifier socket tabs.
Should it not be referenced to ground?

From the PT, both 6.3v legs are run to the 1st 6v6 pins 2/7, then jumped to the 2nd 6v6 and a double leg(untwisted, red/blue) run to the 6sl7 pins 7/8 from the 1st 6v6.
Its hard to see the jumped connections in the pictures or w/ the naked eye but I've traced all the wiring at least twice now.
I have plenty of shielded green cloth covered wire to rerun the long legs, if it is noisy or hums. May do this anyway just to make it a little easier on the eye.


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Post subject: Re: 1951 National 1610 by Valco
Posted: Thu Feb 16, 2017 1:59 am
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sfceric64 wrote:
I have plenty of shielded green cloth covered wire to rerun the long legs, if it is noisy or hums. May do this anyway just to make it a little easier on the eye.


Might not be a bad idea, especially if you have to troubleshoot the heater line later on down the road.

Arjay

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Post subject: Re: 1951 National 1610 by Valco
Posted: Thu Feb 16, 2017 12:21 pm
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sfceric64 wrote:
The heater line does have a CT and its sent to ground @ one of the rectifier socket tabs.
Should it not be referenced to ground?

From the PT, both 6.3v legs are run to the 1st 6v6 pins 2/7, then jumped to the 2nd 6v6 and a double leg(untwisted, red/blue) run to the 6sl7 pins 7/8 from the 1st 6v6.

Its hard to see the jumped connections in the pictures or w/ the naked eye but I've traced all the wiring at least twice now.

I have plenty of shielded green cloth covered wire to rerun the long legs, if it is noisy or hums. May do this anyway just to make it a little easier on the eye.


If the heater line has a CT, that is all you need. You do NOT need the artificial CT with 100-ohm resistors from each line to ground. The reason a type of CT is important is to insure each leg carries the same voltage. But, 180-degrees out-of-phase of each other. Then when you twist the two line together --- the hum will be most effectively canceled.

I like single stranded heater lines. They hold the twist much better than multi-stranded wire. If you use shielded wires... ground only ONE END of each line to the same grounding point. Prolly ends closest to the PT. Grounding both ends would prolly lead to a bad ground loop.

Finally, I don't remember if this amp uses 12AX7 or 12AT7 tubes (or 12AU7). When you lift the grounded side of the heater pin (usually pin 9) ---- remember that pins 4 & 5 must be in connected and in parallel to pin 9. Both sides of the duo-triode has its own heater. And should be wired in parallel (to equal total 12.6-volts) from 6.3-VAC lines.

I've done this twisted wiring on most all Champs and VC amps that I've worked on. All the tubes are wired with single green heater line. The other side of heater is grounded. And one side of heater line from lamp and PT is grounded to chassis.

A lot quieter hum at idle, with twisted pair. Though most of these Champs still have a bit of hum, due to single-ended output.

Good luck! :)


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Post subject: Re: 1951 National 1610 by Valco
Posted: Thu Feb 16, 2017 3:41 pm
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Well decided to go ahead and rewire the heater lines and ended up pulling all the WP Caps while in there. Took the better part of 3 hours and was quite the PITA, almost decided to re-wire the whole thing but came to my senses and took a lunch/smoke break and wrapped it up. I also noticed I'm missing a 500pF mica cap, I'll get that taken care of Friday. I'll add a new pic here shortly camera battery is on its last leg.
Image
Quote:
Finally, I don't remember if this amp uses 12AX7 or 12AT7 tubes (or 12AU7).
Single 6SL7
Also tested the WP Caps on my DMM after pulling them, they ranged between .581uF and .839uF. Don't know if they leak or not but they are surely out of spec (.05uF).


Last edited by sfceric64 on Mon Jul 10, 2017 10:06 pm, edited 1 time in total.

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Post subject: Re: 1951 National 1610 by Valco
Posted: Thu Feb 16, 2017 5:28 pm
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A fine job rebuilding that heater line -- looks like factory work!

8)

Arjay

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