favorite old gear to buy for parts

[xm52]

Test equipment is a good source of parts. A great place to find inexpensive gear is at Hamfests. In the US, check out http://www.arrl.org/hamfests.

A HP 200CD signal generator provides a chassis and a lot useful parts. Remove and rearrange a few things, add an output transformer and you have a nice little amp. The manual has some nice chassis shots: 200cd - Bama Boatanchor Manuals Archive - Edebris.com. As a bonus, the older models came with a 5AR4 rectifier tube. Well worth the $25 that I've bought these for.

Another find is a Tektronix 310A scope. It opens like a book to reveal an amazingly packaged piece of gear. Lots of tubes. High quality parts.

[Paul1453]

Thanks for your input xm52!

Broken or unknown test gear has been probably my best source of high-quality parts for cheap.
Competition is slight and prices very reasonable, if you don't mind getting dirty cleaning them up. 

Many people say these are not good candidates for conversion into a guitar amplifier,
but in my mind parts are parts, and high-quality parts for cheap are hard to come by.

Most say converting different audio equipment is the way to go.  Like Bogens.

I'm gonna let this one slide by as it's more amp than I want or need.  Maybe it is something one of you louder fellows might be interested in.

http://www.ebay.com/itm/221936022519

I just got a super clean Bogen K10, and a B&H Filmosound 302 15 watt.
These are more in my desired power output range, and should need very little modification to be rocking guitar amps.
I've got one more item coming into range, and will post that if I take the shot.

That Bogen listed above might be a decent platform for someone interested building a PP 6L6 40-50 Watt output guitar amp.   
That is a lot more output than I need.  Do your own research to see if that Bogen might meet your needs.
There is documentation available online for free for that specific model.   

Somebody wants 5x what I paid for my B&H without a speaker.   
And he might actually get it...   

Another with a more realistic BIN price of 2x + of my cost.
More confirmation for my mind that I got a good deal.   

[Toxophilite]

Paul I'm beginning to think you might be an emoti-con artist.

[Paul1453]

Paul I'm beginning to think you might be an emoti-con artist.

An interesting play on words/symbols there.   

The BIN price on that Bogen is definitely a better deal than this one that just sold on my watch list.

Over $100 including shipping for a Magnavox stereo dual SE EL84s with one channel distorted???   

The way I value items, I'm hard pressed to see over $100 in parts in that.
I like deals where my conservative value of parts is at least 2x the total price I paid.

[Paul1453]

This one is out of my price range, but it is BIN, free shipping and premium tubes!


http://www.ebay.com/itm/Roberts-440-Tube-Stereo-Amplifier-Project-EL84-12AX7-Telefunken-Free-Shipping/391329039518?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D34225%26meid%3D5b6a3442b7f444cebc6bd83c16d0c183%26pid%3D100005%26rk%3D1%26rkt%3D3%26sd%3D151895410007

In parts, I can see at least the BIN price in this one.  Maybe not 2x, you be the judge.

[HotBluePlates]

In parts, I can see at least the BIN price in this one.  Maybe not 2x, you be the judge.

You don't buy that one for parts... you buy it because you're gonna add your own preamp(s) to turn it into a usable amplifier.

That is a power supply chassis which already has 2x EL84 single-ended output sections, complete with a 1/2 12AX7 driver, and output transformers off-chassis. All that needs is a preamp for your signal to drive the output section that's already assembled for you (which originally powered the Left & Right speakers for that tape machine).

The smart money figures out how to take what's existing and go the extra-mile to make it suitable for your use. It is less-sensible to rip it apart, then find you have 5 miles to go to put it back together the way it was (because the parts yielded work best the way they were originally assembled), and then go the extra-mile to make it suitable for your use.

[Paul1453]

In parts, I can see at least the BIN price in this one.  Maybe not 2x, you be the judge.

You don't buy that one for parts... you buy it because you're gonna add your own preamp(s) to turn it into a usable amplifier.

That is a power supply chassis which already has 2x EL84 single-ended output sections, complete with a 1/2 12AX7 driver, and output transformers off-chassis. All that needs is a preamp for your signal to drive the output section that's already assembled for you (which originally powered the Left & Right speakers for that tape machine).

The smart money figures out how to take what's existing and go the extra-mile to make it suitable for your use. It is less-sensible to rip it apart, then find you have 5 miles to go to put it back together the way it was (because the parts yielded work best the way they were originally assembled), and then go the extra-mile to make it suitable for your use.

I agree with that 100%.   

That one looked perfect, as you pointed out.   

I was just saying that the parts alone, even if one had to go 5 miles extra, looked to be worth the price on this.

If I had an extra $150 to drop, it would already be mine.   

[Paul1453]

Making a usable amplifier.  As you can see my most recent purchases are definitely moving in this direction.   
I'm learning.

I'm still of the opinion that, if you can get high quality parts cheap enough,
it is often worth it to go that extra 5 miles.   

The K10 came in today.  Definitely one more suited to modification into a rockin guitar amp.

Major score on the tubes!  I got a Mullard 12AX7, and a Bugleboy EZ80!   
I have stacks of 6AU6s (with 2 Mullards in the bunch) and nearly as many 6AQ5s (no premiums here, but plenty that test above NOS specs).
Overall she's very clean.  I won't get filthy getting it prepared for modification.
Got the tubes out, DeoxIt sprayed in sockets and pots.
Even if I have to change all the caps in this, I should have it rockin before the end of the weekend.   

[eleventeen]

Over the weekend I had a thought.


It may not be especially applicable to tube GUITAR amps. But it would be pretty darn good for building a stereo tube amp with minimum fuss.


Triode Electronics sells "upgrade/rebuild" kits for Dynaco Stereo 35's and 70's. These boards handle everything surrounding the little tubes.


You can buy a naked dual channel preamp PC board from them that uses your choice of 6AU6, 12AX7, 6DJ8 (6922) or any of half a dozen other tubes. Naked board just under $40, with parts (you have to build) for $85. A little high but the sourcing is all done. They have a whole section devoted to Dynaco stuff. They are obviously afficianados. I found it interesting that they have a version that uses 6AU6, a tube you get in large qtys with junk gear but is otherwise semi-useless.


It is true that I could build such a circuit for under $85, but I was thinking the naked PC board is well worth the $40 just to get the thing built in a known, proven, short-lead-length, good documentation supplied kind of way.


The boards are meant to install from the bottom, necessitating a big rectangular cutout on the main chassis. But I see no reason why they could not mount on 4 short standoffs above the main chassis. Poof, instant stereo amp from a carcass.

[Paul1453]

Cleaning and inspection done.

Only one area with two things noted.
Someone's been in here and did a repair/modification.
1st E cap has some bulging corrosion.  It's got to go before I apply power.

[PRR]

> 6AU6, a tube you get in large qtys with junk gear but is otherwise semi-useless.

6AU6 is a hopped-up mini of the 6J7, *the* all-purpose pentode which nearly all sharp-cutoff pentodes are derived from.

FWIW, the BBC made a whole location mixer with 6AU6. Preamps were wired triode using *screen* as anode, and the nominal plate as a grounded shield. Then 6AU6 pentode gain-stage, and 6AU6 triodes for driving a phone line.

6AU6 can generally be used for small-signal pentodes. Adjust the G2 resistor to get plate voltage ratio similar to what you are adapting from.

It is also a fair approximation of a half a 12AU7 lo-gain triode.

It was not aimed for low-microphonic quality. However many of the types once sold for low-crackle have been picked-over and abused so much over time that a "right type" is no assurance either. If 6AU6 are flooding your bench, you can select for low-microphonics. The shakier ones can be strong cathodynes or even puny "power" amplifiers.

[DummyLoad]

6136  & 7543 are subs for 6AU6 - sylvania claims 7543 are low microphonic, low hum, and high rel.

--pete

[eleventeen]

Thanks, PRR. I certainly recall that for the 40+ years I have been messing around with tube junk, 6AU6 are plentiful and I really had no need for them back then, either.


I am thinking, in the context of ordering and using one of the Triode Elect boards, I should get one for 6AU6 and even if none of 20 or so I have are non-microphonic, then NOS ones can probably be bought for $3-4 instead of "whatever the market will bear" for 12AX7.


For the moment and for building a stereo tube amp out of a dual-6BQ5 carcass of some kind (bot one for $5 at the last junkfest and I probably have 2-3 others) these PC boards make a lot of sense and are worth trying.

[Paul1453]

I was hoping to pick up a similar Bogen for cheap tonight.

That doesn't look like its going to happen now.

They've already driven the price half way to crazytown, I can see that's where they're headed.

I'm out now.   

The clown car to crazytown must have broke down.   
The price ended here.  Not a terrible deal.  I should have bid a couple dollars more at the end. 

[uki]

Hey this is a great thing, I also been searching for some deals, and found this one:
Don't mind the language just look at the pics !! 

http://sp.olx.com.br/sao-paulo-e-regiao/antiguidades/valvulas-antigas-de-televisao-25462214
 

[Paul1453]

I gave you guys a shot at this one last week.  I couldn't let it slide by again.

It looks like a little piece of shit, unless you know what it's got hiding inside.   

I call it the SwollenSack by 3M cause it's stuffed with a good tube amp inside.
I'm familiar with these because my Dad worked for 3M and I used one of these as a kid.

These have a 10W PP tube amp inside.  I remember them being pretty loud on just the internal speaker.
For less than $25 for a complete PP 10W tube amp you can't go wrong!
Cheaper than you will find a comparable B&H amp.  Most just don't realize what these have inside.   

[uki]

I got 28(one inside the box, 27 in the pic with all of them) tubes from that deal!! There are some I have no clue what they are but there is like 2 6v6 one is GT, 2 tubes that looks like double triode, 5Y3 is a rectifier yes? 50L6 there is like 2, 2 or more 35Z5GT !!

Got pics !

[Paul1453]

Greetings Uki,

Thanks for sharing your experiences with us.  The point is to learn from each other on this thread.

So with that said, this is my take on buying junk tube lots.

You really have to be careful and know your stuff here.  Better yet, you know the seller and know what type of lots he sells.
You have to get a screaming deal most times for these to work out.  I have posted some of my tube lot buys. 
Mine have averaged less than $0.25 per tube delivered right to my door.
I have found one seller in particular that I trust to buy from.
He packs them properly so none arrive crushed, other seller's haven't and I got some crushed tubes.
I have a tube tester so I can check these untested lots.  His lots always contain over 85% good used tubes.
OK, but have you seen a pile of used tubes pulled from old gear before?  Many are filthy.
Covered with decades of smokey, oily, grime, and dust that smells funny.
So, I usually spend an hour or two unwrapping and wiping down the tubes with a rag and hot soapy water.
Ohhh, guess what, That writing stencilled on the tube will usually wipe right off then.  So you should ID the tube before cleaning.
I then take a permanent Sharpie marker and write the ID on the tube.

So now you have a bunch of clean and marked tubes, great, but are any of them any good for guitar amps?
Usually not.  You definitely are not going to get a box of used Mullard 12AX7s for $25.
Most easily identified guitar tubes are going to be removed from their lots before they sell them.
Guitar tubes go for significantly more than other tubes.  Sellers know this.
I have had a couple Mullard and Bugleboy guitar type tubes slip by into the lots I bought, though.
That's what you are hoping for, one Mullard or Bugleboy can pay for the whole lot.
If you are going to try to resell them (I never do) you need to be careful not to wipe off the markings.

Mostly you are going to get a bunch of obsolete TV or Radio tubes that no one else wants to buy.
Hopefully, you got a few usable guitar type tubes from your lot.
It's a lot of work for mostly junk, but I did get a few premium Mullard and Bugleboy guitar tubes this way.

That's my perspective on junk tube lots.   

[uki]

Good hints!

I got luck on this one , those 2 9 pins pre-amp tubes, are sweet velvet sound like, tested them and then put one at a time in the amp, then I put both in the amp, I got like a new amp now !!

Also i got:

1x 6V6 GT
1x 6K6 GT
1x 5Y3 GT
1x 6AQ5A

Here is the pics of those 2 9pins ones:

[Paul1453]

I think you got a vintage 12AX7 and maybe a 12AT7 in the deal!

It's amazing how a premium tube can change the sound of your amp.
I am glad you are happy with your purchase!   

[Paul1453]

Somebody picked up that Telefunken listing.  I thought it might go quickly.

Was it one of you lurkers.  Please let us know if you got it and how it works out.

The BIN Bogen is still available, for somebody interested in a 40-50 Watt platform.

Or this auction that ends in 4 1/2 days for a PP 6L6 Bogen minus tubes.

http://www.ebay.com/itm/172012831370?euid=5f0c907f9906457ca0b682c8fff322ce&aid=222007&meid=f211ed23b9bd4f63bdaa2219d976a955&cp=1&_trksid=p11010.c100352.m3747&_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=20150112095601&meid=f211ed23b9bd4f63bdaa2219d976a955&pid=100352&rk=11&rkt=12&sd=291625056642

[Ed_Chambley]

If you have a unidentified tube often you can bring the numbers back long enough to read them by putting the tube in the freezer for a few hours, then carefully looking it over at an angle in relatively bright light quickly after removing from the freezer.

There are some basic guidelines from construction too.

[Paul1453]

If you have a unidentified tube often you can bring the numbers back long enough to read them by putting the tube in the freezer for a few hours, then carefully looking it over at an angle in relatively bright light quickly after removing from the freezer.

There are some basic guidelines from construction too.

Excellent tip Ed!   

From the construction of those two, are you able to identify them positively?
Uki told me one had more gain than the other, and I'm pretty sure the long plate one is the velvety smooth sounding 12AX7.   

[HotBluePlates]

From the construction of those two, are you able to identify them positively?

No, other than that they are a 12A_7 type. To determine which type for certain, I'd stick them in a preamp and measure plate output with a known sine wave input to the grid. I'd also do the same with a known 12AX7 to get a quick baseline for actual gain in the circuit used. Separately, 12AX7 and 12AU7 often have similar construction features; though not always, 12AT7 usually has very-different plate construction compared to 12AU7/12AX7.

What can be seen from construction is they are a "Philips-family" brand tube, which would include Mullard, Amperex, etc., but also Matsushita Japan (who built a factory with old Philips machines & Philips know-how, if I have the story straight). There are several indicators that these are from a Philips company, but the most-obvious is the X-shaped seam at the top of the tube envelope.

... I'm pretty sure the long plate one is the velvety smooth sounding ...

Be careful generalizing based on the plate length; all you know for sure from that is the long-plate should be more prone to microphonics. The shorter-plate 12A_7's is a later development to shorten the construction so that it's more rigid, and less prone to microphonics.

[Paul1453]

You guys are a wealth of knowledge.  Thank you for sharing!

I wasn't aware the long plates were more prone to microphonics. 
I did notice some Ebay sellers touting the long plates on some premium tube listings.

Uki had 1 other Philips tube in this lot, PY something.  I think it turned out to be a rectifier.

One of those 12A_7 tubes clearly had a double layer base holding the plates together.

I'm happy that Uki got some premium Philips (MiniWatt?/Mullard/Amperex) tubes in this deal.
He seems very happy with the way these tubes improved the sound of his Korean made EL84 amp.

I just checked my MiniWatts/Bugleboy/Amperex tubes and all have the Philips X marks the spot top.
Some but not all the Mullards had the X.  I take it those are vintage production and not the reissue type.
More valuable premium tube identifying information shared.  Thanks!   

[Ed_Chambley]

I can tell certain construction techniques, but I am much more familiar with companies construction.  The Matsushita tube brand HBP mentioned is a good find and nice sounding tube generally.

I prefer RCA tubes mostly and while I am a fan of Telefunken Smooth plate 12Ax7 for audio.  In small tubes EL84 I pay the bux for Amperex as they do not distort as harsh.  That is why I run plate voltage close to 300VDC or less on them cause I want them to last.

I do like EI's and have grown to like RCA "pan" getter. 

Also, I am a tung-sol freak and like every one of theirs especially the 6V6.  I just put a matched set in a 5G9 head and used it this weekend playing and I have to say the transition from clean into distortion is hardly even noticeable.  Very musical and still keeps a openness to chords and I was playing a ES335 Travis style.  Have to say I was impressed.

[uki]

You guys are a wealth of knowledge.  Thank you for sharing!

I wasn't aware the long plates were more prone to microphonics. 
I did notice some Ebay sellers touting the long plates on some premium tube listings.

Uki had 1 other Philips tube in this lot, PY something.  I think it turned out to be a rectifier.

One of those 12A_7 tubes clearly had a double layer base holding the plates together.

I'm happy that Uki got some premium Philips (MiniWatt?/Mullard/Amperex) tubes in this deal.
He seems very happy with the way these tubes improved the sound of his Korean made EL84 amp.

I just checked my MiniWatts/Bugleboy/Amperex tubes and all have the Philips X marks the spot top.
Some but not all the Mullards had the X.  I take it those are vintage production and not the reissue type.
More valuable premium tube identifying information shared.  Thanks!   

PY82

Here is the full list(or almost):

35Z3   -   5x

BSA6      (not sure about this)

6AQ5A   -   1x

6SA7   -   2x

6BA6   -    2x

6SQ7 GT   -   1x

7A8   -   1x

12AT6   -   1x

12AV6   -   1x

12BH7 A   -   1x

12SK7 GT-   1x

25L6 GT -   1x

25BQ6 GT-   1x

50L6 GT -   3x

PY82   -   1x

6K6 GT   -   1x

6V6 GT   -   1x

5Y3 GT   -   1x

12___   -   2x

[Paul1453]

I took a shot at some premium tubes.  $56.77 including shipping for 100 Euro tubes.
As long as they are not all duds, I should come out ahead on this:

http://www.ebay.com/itm/100pc-Euro-Tubes-Mullard-Amperex-Philips-Brimar-Telefunken-Siemens-Valvo-/151899460817?_trksid=p2047675.l2557&ssPageName=STRK%3AMEBIDX%3AIT&nma=true&si=LztFkZLUeQr5FYrG0fWMaW3iHM8%253D&orig_cvip=true&rt=nc

I could see at least 1 Mullard 12AX7 a number of Mullard 6AU6s and I'm hoping one of the Octals is an EL34, I don't have any of those.
I only need a few good ones from this to break even.   

[Paul1453]

OK, no big whiney fest here, but I did get the EURO tubes today.
You take your shots and learn to live with the results.

What I thought was a 12AX7 turned out to be another of those 7247s.
Got a few Mullard 6AU6s and what else?

Like about 8 magic eye indicators, how many of those does one need?
Lots of shiny silver Holland tubes to add to my collection of who knows what these are good for.   

Not a 12AX,AU,AT7 in the bunch.  No 6BQ/AQ5s, and of course no big power tubes like EL34/6L6.
When you buy from a frequent tube seller this is about what to expect.
They know what is good and sells for big money, and will sift that out for sure.
Some sellers do have tons of old pulls that they don't want to bother going through, keep an eye on these guys.

People who sell junk gear usually have no idea if the tubes in their gear are valuable or not.
This continues to be my best source of used premium tubes.   

[HotBluePlates]

Not a 12AX,AU,AT7 in the bunch.  No 6BQ/AQ5s, and of course no big power tubes like EL34/6L6.
When you buy from a frequent tube seller this is about what to expect.

You gotta be careful about getting caught up in excitement on ebay. If the seller doesn't catalog what they're selling, you should assume there's nothing but t.v. tubes in the lot (unless you see something you're sure is desirable; even then you likely don't know it isn't dead).

[Paul1453]

Not a 12AX,AU,AT7 in the bunch.  No 6BQ/AQ5s, and of course no big power tubes like EL34/6L6.
When you buy from a frequent tube seller this is about what to expect.

You gotta be careful about getting caught up in excitement on ebay. If the seller doesn't catalog what they're selling, you should assume there's nothing but t.v. tubes in the lot (unless you see something you're sure is desirable; even then you likely don't know it isn't dead).

I know, just illustrating my adventures.   

What's a good used Mullard 12AX7 worth $30-$40, Mullard 6AU6s maybe $10.  So I could see close to my price including shipping if just these tubes were good.
Lot's of upside potential with 90+ more tubes to go through.

I had never bought from this seller before, probably won't again.
I should have known when he wrote "Lots of money to be made by sorting through these".
That there was more likely little or no money to be made.

I did get a couple of EL91s and EL95s in there.  I can use one of those for my little Norelco R-R instead of the 6AQ5 I subbed in.
I haven't sorted and researched all that I got in this lot yet.  I'm considering it a break even deal at this point.  No major score here.

Back to watching for junk industrial/military gear that can be had for less than $50 including shipping.
Amazing how often that stuff has premium tubes and other high quality parts in it.   

[Paul1453]

About 4 hours left on this one.  I know they look like little POS, but there is a complete 10W tube amp in there.   

http://www.ebay.com/itm/141847571950?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

It's less than $35 including shipping to my location.  I can't get a new 10W PP OT shipping included for that.
I'm out of ammo again.  Got an Oscope, signal tracer, and HP pulse generator on the way now.   

If this POS is working it doesn't need any modification to be a guitar amp.  Plug your guitar in the mic jack, a better speaker on the output and you're rock-n-rolling. 

[eleventeen]

You know, if you are really a junk hound (and believe me, I have been for most of my life and sometimes do and sometimes don't acquire junk) you should check out your local Craigslist. There are some rudimentary search tools on CL.


The thing about a CL sale is:


search for tektronix, hewlett "ham radio" "oscilloscope". (There are millions of scopes for sale. Don't overpay for a junky old tube scope, there are really not a lot of usable parts. Old Dumonts use more 12AX7s than other scopes but sheesh, they are 50 years old now.
obviously no shipping charges
little better idea of what you are buying
that other thing or twelve sitting in the corner
that box of wires thrown into the deal


I would posit right here and now, you could find a tube Conn organ for free or for $25 that would be equivalent to about 6 of your current deals. The issue is can you move the thing. Or a Lowrey. Or a Wurlitzer. I don't really like to break apart Hammonds even if they are stupid organs like the S-6.


*Schober* organs are chock full of 12AX7. Gold mine. Most other organs are full of 12AU7.

[Paul1453]

I have an ad up for old junk gear on CL.  I also check for deals once every 2 weeks or so.

Problem is Louisville is a 1 hour drive each way.
Minimally valuing my time and fuel means I have $50 into going to get something for free.
In light of that, the Ebay purchases I make don't seem so bad.   

[eleventeen]

Here's a free scope.

[Paul1453]

Junk test gear comes through again! 

I know most of you think I'm crazy buying this kind of stuff.   

HP 214A Pulse generator.  Got to love the junk HP gear.
26 tubes total in this thing.  I knew from the manual it had 3 12AX7s.
Most of the tubes in this were Amperex Euro (Gt. Brittain/Holland/Germany) tubes.

So 3 vintage Amperex 12AX7 tubes more than covers my cost on this.   
I knew that going into the deal.

Pleasantly surprised to see that Amperex 6DJ8s go for $15 a piece.   I got 9 of them.   
Even if I sell them at a discount of $10 a piece I will have doubled my money and got my 12AX7s for free.
The 2 7534 tubes should easily bring in another $25.  Still more tubes included, but I'll stop here.

Then the high quality PT, pots, switches, resistors, etc. are just icing on the cake.

I'm thinking this one just paid for my newly acquired used Oscope and Signal tracer.   

[uki]

What ?!?!  26 tubes, plus components, and more more for just 20 bucks !!!   

That is a good deal no doubt !!!

[Paul1453]

Well almost $46 including shipping, but:

Parts are parts, and Premium Quality HP parts for cheap are hard to beat!   

Sometimes the sum of the parts is greater than the whole.
That is a rather unusual PT, with 3 separate HV sections.
Another rarely seen part was an AC input noise filter.
That might be useful if you used a gas AC generator at an outdoor event.   

[eleventeen]

Pretty nice!


One has to wonder if it's possible to make an adapter so that 6DJ8's could be used for 12AX7. (answer = yes) Just have to fiddle with the filament, all the other pins are the same. Sell 'em or use 'em, the value of the piece is mostly in the tubes...and the knobs.


When I looked up the manual for that piece I noticed that (at least the one version I found) the printing date was 1975. That seemed a little odd, for hp to have had tube *anything* hanging around, eg, still in the catalog in 1975. Probably part of it is, they were gov't approved and their stuff would sell for 3+ years after they discontinued it because of the way the gov't bids things.


You'll generally find the transformers to be a little odd in hp gear. The thing to note in test gear is that the power supplies are not built to handle big excursions of power like audio amps are. What this means in practical terms is that the tranny might very well supply say 275 volts post rectifier because that's all a pulse generator that (surprisingly) can make a 100 volt pulse needs. Just saying, I have generally found salvaged hp transformers to be kind of problematical because they won't make 350 volts. OK, voltage doubler. Now you come out of the rectifier with close to 600 volts.


OK, so it would be a great tranny for....say a reverb unit. Or say a 6G2 Princeton. Except it's a big fat tranny  that's way oversized for a reverb unit. Most hp PT = problem child.


I am only telling you this to relay my experience (tho I have never taken apart a 214A) that the PT voltages from test gear are very often goofy for amp use, not in any way to criticize your scrap hunt. If you can make out on the tubes, go ahead, it's pretty cheap entertainment. The other remarkably high quality parts......you'll seldom use.

[Paul1453]

One has to wonder if it's possible to make an adapter so that 6DJ8's could be used for 12AX7. (answer = yes) Just have to fiddle with the filament, all the other pins are the same. Sell 'em or use 'em, the value of the piece is mostly in the tubes...and the knobs.


When I looked up the manual for that piece I noticed that (at least the one version I found) the printing date was 1975. That seemed a little odd, for hp to have had tube *anything* hanging around, eg, still in the catalog in 1975. Probably part of it is, they were gov't approved and their stuff would sell for 3+ years after they discontinued it because of the way the gov't bids things.


You'll generally find the transformers to be a little odd in hp gear. The thing to note in test gear is that the power supplies are not built to handle big excursions of power like audio amps are. What this means in practical terms is that the tranny might very well supply say 275 volts post rectifier because that's all a pulse generator that (surprisingly) can make a 100 volt pulse needs. Just saying, I have generally found salvaged hp transformers to be kind of problematical because they won't make 350 volts. OK, voltage doubler. Now you come out of the rectifier with close to 600 volts.


OK, so it would be a great tranny for....say a reverb unit. Or say a 6G2 Princeton. Except it's a big fat tranny  that's way oversized for a reverb unit. Most hp PT = problem child.


I am only telling you this to relay my experience (tho I have never taken apart a 214A) that the PT voltages from test gear are very often goofy for amp use, not in any way to criticize your scrap hunt. If you can make out on the tubes, go ahead, it's pretty cheap entertainment. The other remarkably high quality parts......you'll seldom use.

Like a toroidial input/output transformer. 

You made me run to the 6DJ8s data sheet.  OK, so it's not quite a 12AX7 sub.  Amplification factor only 33 not 100, but do they also have a sweet sounding output?

Of course, the 12AX7s are actually 12AX7WAs which I had to look up too.  Interesting heater upgrade circuit for Mil application/specifications.  All 3 tested low on my tester, but remarkably balanced and consistent.   I no longer concern myself with the testers readings, especially when they are balanced and consistent across tubes like these.  So the real test is to put them in an amp and listen.  Well, these 3 are right on par with my Mullard or Bugleboy.   

Most people don't consider knobs, but this type with 2 allen screw locks are great!  Also, the pots are on a completely different level from most other guitar amp/consumer type gear pots.

I might have to try a few breadboard prototype circuits replacing 12AX7s with 6DJ8s before I decide whether to sell them or not.   

I don't think I will need/use the 4 big tubes, but now will need to closely check the data sheets and forums before just listing them on Ebay.    
Thanks   

[PRR]

> odd, for hp to have had tube *anything* hanging around

This was bleeding-edge in 1963. 13 NANO-seconds rise/fall?

It was many years before transistors could touch it for speed.

It was decades before transistors could touch it for 100V(!!) output with such speed. It also peaks at 2 Amps. The output stage is a bit more like a transmitter than a plain signal generator. Those are rather unusual output tubes.

Meanwhile it musta got wrote-into many test specifications. If you wanted the contract to calibrate radar SL-987 or nuclear counter XYZ-123, you had to have a "HP 214A or equivalent". And I bet there was no exact equivalent. So buyers would pay HP's price. Being a proven product, HP would be unlikely to re-design until they saw a way to make it 10 times better. They did have slower weaker and much smaller transistor pulse generators. Probably a long time before they beat this combination of size, SPEED, and POWER.

Both the output tubes and the known-genuine 6DJ8 are valuable. Please don't "sub for 12AX7". Don't even handle them. Hi-Fi nuts are crazy for them. 6DJ8 is "just a TV tuner tube", but the best of the bunch, meaning all the genuine ones are long-gone and every dang bottle with the same pinout has been re-badged "6DJ8", no matter how unlike a true 6DJ8 it is. The re-marks have given 6DJ8 somewhat of a bad name (because so many 6DJ8 preamps 'sound' like a low-price TV tuner, because that's what's been stuck in them). But true 6DJ8 fans will cream to get bottles you document to have come out of unmolested 1970 HP gear.

[Paul1453]

But true 6DJ8 fans will cream to get bottles you document to have come out of unmolested 1970 HP gear.

Once again you come through with the inside scoop on all things tubes!

Thank you very much PRR!!!   

I did notice some of them were the gold pin type.

[eleventeen]

The ckt for that hp 214A definitely has some interesting aspects. Tubes with -75 volts on the plates? Hey, no problem, there's -275 on the cathodes, LOL.


You're right PRR, that piece had some pretty impressive specs even 30+ years after it came out. And yes, the output tubes are very unusual.

[PRR]

me> I bet there was no exact equivalent.

CMC Ruthrford model B7B Pulse Generator seems to be remarkably similar, but lower-cost. TV H-sweep tubes instead of the exotic EL130.

Company still in business (unlike HP Test).
http://www.itsamerica.com/Files/history.htm
"The Story of the Radar Range Simulator" 2/3 way down page

[DummyLoad]

Company still in business (unlike HP Test).

thought they became agilent after HP spun them off on their own, then they were bought outright.

--pete

[DummyLoad]

reply 187 -


pics with the power transformer: looks like it has a resonance winding  [ 50/1KC ]. so part of a ferroresonant regulated supply?


--pete

[PRR]

> there's -275 on the cathodes, LOL.

There's no possible transformer for these pulses. (One use is revealing the faults of the best available pulse transformers.) So the load is a choke, made with coaxial lines. For safety this needs to be at zero V DC. As you say, no problem, take the cathodes way negative.

The ITS/Rutherford site says the Navy was buying stuff like this well into the 1980s, buying parts at least until 2002. And concerned that it be an exact equivalent to the originals.

> thought they became agilent

Well, yeah. I'm still disgusted they dropped the H-P name, let the PC division have it. Rolls Royce Jets was kind enough to license the R-R name and badge to VW or BMW or whoever bought the dregs of the car spinoff.

[DummyLoad]

I'm still disgusted they dropped the H-P name

me too. they could have kept the name as long as they only made test equipment under the name: certainly that wouldn't have caused any issues. damn sue happy legal buzzards.



--pete

[Paul1453]

I'm still disgusted they dropped the H-P name

me too. they could have kept the name as long as they only made test equipment under the name: certainly that wouldn't have caused any issues. damn sue happy legal buzzards.



--pete

I think the computer division has actually destroyed the Good HP name.

I have said I used to say HP stood for High Priced, but it also stood for the best scientific test equipment money could buy.

Their gear was very expensive, but the only brand you knew you could trust.

[Paul1453]

Well after the favorable 6DJ8 feedback I got here from you very knowledgeable guys,
I decided to give another HP 214A a go.  I had to pay a little more this time, but still should profit nicely.

I might have found a funding source for my other junk gear purchases.