favorite old gear to buy for parts

[Paul1453]

I have bought a number of junk R2R recorders.

Most are SE 6V6 or 6AQ5 output circuits.

The OTs are usually 2.7K load at 8 ohms.

Obviously, I could make Fender Champ clones from these.

I wasn't quite satisfied with a 6V6 or 6AQ5s output.

I found another circuit that I like much better now.

An EF86 driving a metal 6L6 with a B+ of 250 VDC.

The 6L6 data sheet shows numbers for +250 V.

6.5 Watts output power seems to be fine with these little SE OTs.

At 250 V on my BB, I have no oscillation issues.

This sounds much better than a basic Champ to me.

I haven't tried any modifications yet.

Maybe the EF86 could be run a little hotter???
Or the 6L6 bias resistor could be reduced from the 265 ohms I used???

My bench supply says I'm pulling 55 mA of current for the whole circuit.
Data Sheet says 170 ohms self bias with about 85 mA maximum current used.

Any suggestions for improvement of this already well performing circuit?

[HotBluePlates]

... junk R2R recorders. Most are SE 6V6 or 6AQ5 output circuits. The OTs are usually 2.7K load at 8 ohms.

I wasn't quite satisfied with a 6V6 or 6AQ5s output. I found another circuit that I like much better now.

An EF86 driving a metal 6L6 with a B+ of 250 VDC. The 6L6 data sheet shows numbers for +250 V.

... the 6L6 bias resistor could be reduced from the 265 ohms I used??? My bench supply says I'm pulling 55 mA of current for the whole circuit. Data Sheet says 170 ohms self bias with about 85 mA maximum current used. ...

Don't confuse "Zero Signal" with "Max Signal" numbers on the data sheet (unless you're measuring while playing full tilt). The old sheet shows 80.4mA total cathode current at idle. That's 170Ω * 0.0805A = ~13.7v bias at idle, shifting to/above ~14v at full tilt (due to distortion/rectification effect).

The real question is do you know what current your R-2-R power transformer can supply? You'd like to know if it can support the extra draw from the 6L6 (both on the B+ and the heater, which is doubled from 0.45A to 0.9A).

Even if it can't go all the way to the data sheet maximum condition for 6.5w output, the output of the present setup probably give you very similar sound-in-the-room.

If you could draw the extra idle current (by dropping the cathode resistor to ~170Ω), the 6L6 would be slightly easier to drive (~13.7v for 80.5mA through 170Ω vs. ~14.6v for 55mA through 265Ω).

[Paul1453]

Changed bias resistor down to 172 ohms.

Now the PS is pulling around 70 mA.

It is a little louder, sounds a little better to me.

The difference to me is the clean volume.

The 6L6 stays cleaner longer and louder, but can still be overdriven.

The metal 6L6s get really hot though.

They need to have good ventilation in a small amp.   

I'm thinking most of the R2R PTs  have should be able to power this 2 tube circuit.
Most of them had 4 or 5 tubes to power in their original design.
They were usually using a B+ near this +250.
I'm sure some of my PTs won't work for this.
But I think a number of them will.   

[Paul1453]

For a SE output, I'm liking the sound of the 6L6 or bigger tubes better.

I like the 6V6/6AQ5/EL84 in PP configuration.

If I can get away with using most of my little SE OTs with a bigger tube I'll be happy.

I'll just have to pair up the little guys and get PP OTs for them.   

[Paul1453]

Checked the Data Sheet for the EL34.

At 250V it has 11 Watts output at a 2K load.

Too much wattage for these little SE OTs, and not quite the right load.

Looks like a KT66 might work with 7 1/4 Watt output at 250V with 85 mA @ 2.2K load.
I don't have any of these anyway.

I put all my metal 6L6s and my 2 6L6Gs through this circuit.

1 6L6G and 1 metal 6L6 pulled 75 mA of current.

All the others pulled 70 mA.

Every single one of them sounded really good to me.

Much better than a basic 12AX7 6V6 Champ to my ears.   

[Paul1453]

I checked my circuit voltages with my DMM, for more accuracy.
My bench PS showed 250V on its analog meter.

I got:

A = 258
B = 257
C = 255

What should I expect if I dropped the C node feeding the EF86 down some?

It is sounding really good to me at these values.
It is still on the BB so making little changes is quite easy.
Going just by ear, many small changes result in an imperceptible change in tone.   

[Paul1453]

Got some new toys to play with.

For $16.99 delivered, I decided to find out for myself about the little SS PA amps.

Now for the Bell PA.

Bell Sound Systems of OH, tube PA Model 5630.

I searched for the schematic online, Radiomuseum seems to have it but I'm not a member.
I couldn't locate it anywhere else for free online yet.
If one of you are a Radiomuseum member and wouldn't mind downloading this schematic for me.
I would greatly appreciate it.
Don't bother with this.
If I want to sell it to the Army I figure I'll need to include the manual.
Searched Ebay and got a good deal on one, $6.25 delivered.  Done.

My plan for the Bell is to just restore and revitalize it with a new custom military paint job.
Then see if the Command here is interested in a cool USA made, restored and custom painted, PA tube amp.
My 2nd son just graduated from the on post HS.
The 500+ people in attendance at the Parade Field could not hear the speakers due to the crappy SS PA they used.
They might actually be interested in a better quality sounding tube PA with a custom Military paint job called the "Liberty Bell".   

[kagliostro]

Now you can download 3 schematics a day from Radiomuseum for free

Chose the apparatus you are interested on, click on the small image of the schematic that appears on the right, a bigger partial image of the schematic will appear, click on this image, insert your data and receive an e-mail with the requested schematic

Pay attention that if the schematic is splitted in more images you must repeat the procedure for each piece (remember 3 per day)

Ciao

Franco

p.s.: You have a Private Message

[uki]

Hey guys I got a nice one here. 1956 Tape recorder !

Model: 711 Tape-O-Matic - V-M VM Voice of Music
Valves / Tubes  6: 12AX7 12AX7 12AX7 6SN7GT 6V6GT 5Y3GT

One of the 12ax7 ,the print wore off, does anyone recognize the brand ?

Check it out :

[eleventeen]

Looks like CBS (left)  Tung-Sol (right) to me (lower pix) Upper pix looks like a Japanese tube.

[Paul1453]

Sharp eye 11!   

I missed figuring out the Tung-Sol, but now that you pointed it out.
I think that is what that has to be.

Most of my MiniWatt labeled tubes are from Holland,
but Philips could have made some in Japan.

I have some X marks the top 6DJ8s made in Japan.  HP labeling I think.

[uki]

Looks like CBS (left)  Tung-Sol (right) to me (lower pix) Upper pix looks like a Japanese tube.

Nice catch !! I still have to do the freezer trick , maybe the full print will show up.

[eleventeen]

CA Historical Radio Society flea market tomorrow. I am really in de-accumulate mode and I dropped off a lot of stuff as a donation. But I saw two or three rooms of gear that was going to the flea market and there were some audio amps there with Fender Bassman trannies.  The trick is to not buy back the same crap you just dropped off for donation! 

[jojokeo]

What should I expect if I dropped the C node feeding the EF86 down some?

A bit late on this, it's a very long thread so I only check it out occasionally but...it's nice to see little treasures coming out of old gear. Also nice to see them not end up in the trash somewhere. But even with the best intentions I've managed to make a mess of things sometimes like having two superb ANOS black plate triple mica square getter 5751s. I got so excited, carefully cleaned them, and took them to my kitchen door to get a good view in the direct sunlight and I fumbled one right at the goal line. As it fell I tried to save it from hitting the hard unforgiving tile floor using my best hockey goalie and soccer style moves but it still hit hard enough in the right manner to break.      a dumb $50 mistake give or take.

Lower voltages on a EF86 usually help cause it to break up earlier and lose headroom. Sometimes it can also help it to become or show more microphonic behavior as well by increasing it's gain. Since '86s have plenty of gain anyway I like running them at higher voltages and lower gain conditions and even running them clean in triode mode is like a really good 12AX7 stage. 5879s are also very nice which can be found in Bell & Howell equipment.

[eleventeen]

Yeah, similar happened to me. I bought one of those early Tektronix 555 2-man scope power supplies at the last CHRS flea market for $5. One of these:


http://www.lemis.com/grog/Albums/Tektronix-555.php  very bottom of page.


It looked like it was in decent shape. When I got it home, I could see some of the tubes were cracked. The 6080's? Nope. The 6AU6's? Nope. 3 out of 3 12AX7s were cracked and 2 were 5751! Argggggh.


Did decent at the flea market:


I *did* get the Fender-transformer thingy I saw, $35 for a 4-6L6 type amp with a HUGE Sunn (yes, branded "Sunn") power trans and a Fender Twin OT. Untested, build quality  looks just a bit above average, who knows it might work.


$5 for a Heathkit IG-18 audio gen, untested but looks decent


$5 for a nice  resistor decade box. 


$5 for an unknown chassis with 2x RCA/GE 12AX7 and 4x RCA/GE 12AT7 and that number of Fender-type tube shields.


$$ damage not too bad.

[eleventeen]

One of my best scores evah!! Fun.


hp 711A Power supply. I have wanted this particular model for a long time because it is small and will fit under the bridge on my bench. 500 v, 100 mils. Kewl. $5. Oh yeah, has 2 qty GE 6L6GC as pass elements. Very excited.


hp 521 counter. I know it may sound weird but I have wanted a counter like this (using the 4-12AU7 decade counters....either Beckman or Berkeley Scientific) ever since I used to wander onto Canal St in Lower Manhattan and find the internal decade boxes. That would be like almost 50 years. This was among the very first electronic counters that were available. With 7 extra decade boxes....and now....guess where all my Conn organ 12AU7s can go? Each decade uses 4 of them! $10.


Solavolt variac and constant voltage transformer. 50 lbs, in its own box.  $15.


The other thing is A LASER!!! Free.


All this for $30. I am supposed to resist this incredible pile of crap??? No way.

[Paul1453]

You always seem to find the deals!

Now you just need a tank and shark to mount your laser on, Dr. Evil.  LOL

[eleventeen]

I'm always searching on CL for "oscilloscope" or "ham radio" or "vacuum tube" or "test equipment" or "organ" or "free organ" or "tube amp" and sometimes there's something there, often there is not. Had to drive 30 miles but the asking prices were silly cheap. There was no mention of the 521 counter nor laser in the ad, the counter was $10. Could not resist that (At least 20 12AU7s)  I really only wanted the power supply as I had been looking for one for a while. The variac/CV transformer I really have no need for as I already have a variac, but $15 was just too cheap to pass up.

[mresistor]

eleventeen - I had two older hammonds I could have gotten for free in the last month. but I sold my 2x pickup and have no way to pick them up. So I had to pass. They were both tone wheel organs, although not B3s or the like. I think they were L series.

[eleventeen]

I dunno, I kind of dislike the idea of taking apart old Hammonds, even if they are dirtballs like S-6 chord organs. I know they will require more effort and and time and $$ in service to make them work than they will ever be worth....and let there be no doubt, there is IMO no better source of (more, a greater quantity) used parts and stuff than old organs. I just don't like the idea of trashing the Hammonds and I'm not that happy about the amps you get of them, should you dismantle. I don't feel that way about CONNs or Lowreys, etc; I know the next guy will cheerfully take them apart and I don't criticize them....it's just that I myself kind of don't like to do so. Yes, it's weird. And surely, many are destined for the dump so what does it matter what I think? The other problem with organs is that they generate half a pickup truckload of crud you have to cart away.

[eleventeen]

I thought would comment on the hp 711A and 521 pieces I bought for so cheap about 5 posts upthread.


Both items kinda sorta worked; After variac'ing them up, the power supply only went to 270 volts, the counter neon lights lit up but the counter would not self-test properly and was otherwise frozen. I opened them up and each one had 2-3 bumblebee caps. I lifted one end of all of them and half were sort of leaky. I shotgun-replaced 3 of those caps in one and 3 of those caps in the other and voila, both items work fine now.


Those caps are quite simply "always suspect".

[vibrolax]

I thought would comment on the hp 711A and 521 pieces I bought for so cheap about 5 posts upthread.


Both items kinda sorta worked; After variac'ing them up, the power supply only went to 270 volts, the counter neon lights lit up but the counter would not self-test properly and was otherwise frozen. I opened them up and each one had 2-3 bumblebee caps. I lifted one end of all of them and half were sort of leaky. I shotgun-replaced 3 of those caps in one and 3 of those caps in the other and voila, both items work fine now.


Those caps are quite simply "always suspect".

I bought a "working" 1958 HP-400D AC VTVM about 5 or 6 years ago for $15.  The electrolytics in the power supply were fine, but all the coupling caps (scarlet colored Chiefs, IIRC) were leaky.  I shotgunned them all, and it worked fine.  Darn, HP wrapped those leads around the terminal strip lugs very well.

[eleventeen]

Who lives near Poughkeepsie, NY and likes to scrounge old tube stuff?


Good pile of crap: $59. The hp transfer oscillator has a lot of good parts.


http://www.ebay.com/itm/LARGE-VINTAGE-LOT-NAVY-Signal-Corps-HP-OSCILLATOR-Oscillograph-More/201657184860?_trksid=p2046732.c100040.m2060&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20140107095009%26meid%3D08bb69528ece42a7a0f6828332f48f7e%26pid%3D100040%26rk%3D2%26rkt%3D4%26sd%3D262587435023

[eleventeen]

OH THIS IS PROBLEMATICAL!





Here's an organ speaker cabinet with a dual 6550 tube amp in the bottom for $125. Check out the GZ34 with metal base. Yow!


Metal based GZ34 sell for over $200 on ebay. That tube would pay for the whole thing and 2-way gas.


It's only 185 miles away. Yeah, there's a funky looking 15" speaker and a horn and a HUGE crossover network too.


I just may have to go get this.

[Paul1453]

The vintage GZ34s are insanely priced on Ebay.

What gives, is it some kind of tube fetish or what?

It is just a rectifier tube after all.

I just picked one up tonight, hidden in a larger lot of 65 tubes for a total price of $26 delivered.   

[eleventeen]

Well, there's fetish and there's fetish. But you can find half a dozen examples of metal-based GZ34 not just selling for but which actually sold for upwards of $200 so I don't argue. I am frantically looking for other tubestuff located where this cabinet is to see if I can get more junk on the trip.

[jojokeo]

... I couldn't let it slide by again.
... I call it the SwollenSack
... For less than $25 you can't go wrong!

It's taken almost a year and a bit over $27 but persistence pays off? We shall see? I haven't got it yet to see what it's all about but thanks for tip!? Do you do anything special with these or just scavenge out what you can use?

[Paul1453]

JoJo,

There are a few different designs of these, some SE some PP, but all usually contain 3M labeled Mullard GB tubes.

I have just modded one of these, and have another still in my pile.

It's a heavy beast that doesn't look much like a guitar amp as it is.

I plan on stripping the parts to put in a more traditional design in the future.

Plenty of quality parts to justify your $27 delivered price.

I think you will be satisfied.   

[super&plexi]

Knight pwr/pre, vol, treb bass, beautifull shape, cage-tube cover looks New w/quick coat of grey primer from can...110.00, w/2 Millard el84's, &2 bugle boy 12ax7's!!! All strong, no mention of them in ebay ad. Goodwill 25.00 R2Reel, Grundig/Concord, something like that...2 more bugle boys, 12ax's, 2 6ca7? ...the ones people make the headphone amps out of, and an intact 2 Speed Motor that looks just like the ones that come out of the vibratones, along with tons of heavy duty metal, angle , n high quality CC resistors and rotary switches like2  pole, 6,8,10 throw... heavy duty cast frame speakers, albeit small like 6 or 8 inches, and a large heavy duty cabinet suitable 4 a portable extension cabinet or with the metal mesh vents,a vibro type cab. The thing was silly heavy built like a tank. Also a couple of view meters.... the Knight sounds great...mono, love to get another one, run 1 on it's own  speaker, dual mono block style. It only needed a cap can change. Actually only 1 of  the smaller value ( something like 20uF @ 150) had gone bad. The higher voltage and microfarad Elektrolytics, and one smaller value in the can we're okay but I just changed them all. As far as the jrc4558 chips they are in all kinds of stuff cheap radios and the boss red power supply. Those rip offs of the scholz Rockman have a few MN 30007 and whatever variants... they are those red housing rip offs of the scholz Rockman, but if you're into that they actually sound pretty good. I love old broken computers for their power supplies ribbon cable push button switches that are like the same ones on DigiTech multi-effects, not to mention some have a great fans.. and those Square switching power supplies make great bench power there's a bunch of tutorials on YouTube you basically just run the little female connectors that Doug sales here, the kind that fit your probes and a way you go.

[eleventeen]

Next victim:

[jojokeo]

I think you will be satisfied.   

Que the French horn...Waa waahh. I got hosed in that I was unaware these were actually made with transistors too. Who knew? My own fault for not asking questions I guess? But people selling these things don't know anything about them either. Buyer beware...

[eleventeen]

As one who trades stocks for his living, all I can tell you is, make all the $27 mistakes you possibly can.

[jojokeo]

Ha! Yeah not a big deal at all. I can either test it out and who knows maybe even have a 10w or so transistor amp?    I could employ it for the rare occasions I need to signal trace something? Or need to record a super clear pristine jazz passage?    Or who knows maybe someone else will actually want it and buy after knowing it at least works or for parts? please see below:
 
Notice - For Sale: one fine *SS/SwollenSack tape recorder for cheap???
 
 
 
 
 
*(SS=solid state)

[eleventeen]

I really try not to buy stuff on ebay unless I know for absolute sure its toob. I just hate paying shipping. Vastly prefer Craigslist. I am not saying I like driving 400 miles like I had to for that cabinet, above, but that worked out nicely. The metal GZ34 tests as if brand new and I mean brand new, and the 6550's test about 95%. As for the scope, I am working with the seller who lives about 150 miles away, he occasionally drives down to my area. That scope has 22-24 6DJ8 in it. And 4-5 12AX7s. The plug in has 3-5 12AT7.


Sometimes those old Tek scope plug-ins have some nice parts. But you have to get them cheap and if they are $25 to ship, it doesn't work. 

[uki]

Check out this hit guys !! Traded for a old computer and printer !!

Looks like it does have a PP 6v6 power amp, a 6K6, the recto tube is a 5U4, looks good for a conversion !!

Geloso radio with pickup.

[kagliostro]

Nice

Model of the radio ?

Franco

[Paul1453]

Looking good Uki!

I haven't been posting much lately,
but here is my most recent Ebay buy.

Another great deal.  ;^)

[uki]

Nice

Model of the radio ?

Franco

No Idea, I'm too wanting to know that, so to search for schematic would be easier, the only Obvious thing about it is the name Geloso, which is Italian manufaturer.

[Paul1453]

K might be able to help you with that schemo.

But if your goal is not to have a radio that can also be used as a guitar amp, then it's likely unnecessary.

If your only looking to convert this to a guitar amp, then you will probably be taking out the radio tubes/circuit to make way for your pre-amp.

The full output section could likely be used as is, and is rather easy to trace and document that section.
With your output section documented, you could look for and likely find many guitar amps that use it or something very similar.
It does appear to be a PP 6V6 output section, so lots of guitar amp circuits will be similar.   

[kagliostro]

Uki you say

2 x 6V6 - 1 x 6K6 - 1 x 5U4

but I count 7 sockets

Which are the other tubes ?

EDIT: Also a good photo of the dial plate may be of some help

Franco

[uki]

Uki you say

2 x 6V6 - 1 x 6K6 - 1 x 5U4

but I count 7 sockets

Which are the other tubes ?

EDIT: Also a good photo of the dial plate may be of some help

Franco

There are 9 total,  2x 6V6GT, 1x 6K6GT, 1x 5U4G, 1x ECH42(out of the socket), 1x 6SG7,  1x 6H6, 1x 6J7G, and another without a print. Look the picture.

[kagliostro]

OK Uki

9 tubes

one, due to the position, seems a magic eye, do you confirm ?

you say 1x 6SG7 and later 1x 6SG7, how many 6SG7 tubes are there ?

the missing tube is a noval and all other are octal ?

--

If you can a photo (a closeup) of the Dial Plate can help to identify the model


Franco

[uki]

@Franco

Ooops that was a misstype!! One of them is 1x 6J7G and 1x 6SG7. Post is fixed.

The missing tube is octal but small socket it is the ECH42 I removed the tube and left it out.

I found this link with many Geloso papers: http://www.arimi.it/storia/bollettini-geloso/

Been looking one by one...

[kagliostro]

OK, also I'll give a search

and I've ask also to some friends, I hope we can find it

Franco

[PRR]

> looking one by one...

"Annuals". (Actually several per year.) Bo100 is a very modern tube and transistor model line. Up past B020 is pre-Octal tube types. First 6V6 seems to be Bo24, but I do not see a rig that fancy. Am looking at Bo26 but I should be outside.

EDIT- that cabinet is possibly post-War. B035 is Autumn 1940. Bo36 is April 1946, early post-War days. Bo36  page 7 shows push-pull 6V6, but not your full line-up (ah, this is a microphone amplifier).

ECH42 appears in Bo45, but in a 6V-12V radio (probably for car). Your ECH42 in an otherwise all-USA lineup is odd. I wonder if it was supposed to be a US type, but tube shortage at factory or in later years caused a change.

I would not have high hopes for "Short Wave", unless you have deep experience restoring old antique radios. The precision tuning needed for >1MHz does not hold up over the years, phenolic breaks, wax sags. Also 1938 SW was CW or AM; today it is largely SSB or code chirps. There must be a few long-range propaganda transmitters still on the air, but fewer every year. (And they probably have a clean reliable web-service.)

[uki]

> looking one by one...

"Annuals". Bo100 is a very modern tube and transistor model line. Up past B020 is pre-Octal tube types. First 6V6 seems to be Bo24, but I do not see a rig that fancy. Am looking at Bo26 but should be outside.

I would not have high hopes for "Short Wave", unless you have deep experience restoring old antique radios. The precision tuning needed for >1MHz does not hold up over the years, phenolic breaks, wax sags. Also 1938 SW was CW or AM; today it is largely SSB or code chirps. There must be a few long-range propaganda transmitters still on the air, but fewer every year. (And they probably have a clean reliable web-service.)

Thanks for the input PRR !!

I'm only interested in the amplifier section of it, I was trying the other day to catch some SW station in a modern radio... nothing.

Several caps about 8 are cracked and bleeding the insides, the schematic would help with the values, at least for the amp section, which looks to be a PP 6v6. No preamp tubes on it, curious, the audio signal goes directly to the power amp ?

[uki]

I have covered so far Bo1to Bo3-4; Bo50 to Bo75; Bo85

[PRR]

AM radio, the detector outputs about 1V of audio. You need one voltage-amp stage to get up to 6V6 grid level.

In days of 78s, a phono pickup was a beast which chewed shellac to make about a 1V signal. You just switched the phono pickup in place of the AM detector.

For guitar you want one more stage. You can re-purpose an IF stage. Triode-strap the pentode and use Champ-like cathode and plate loads.

[PRR]

Bo31, Super G.91, is push-pull 6V6, paraphase inverter, basic AM/Phono switching. 6Q7 diode runs through IF winding to 0.1Meg to 5-way switch. 4 ways are AM, one way connects the oval FONO input. This to volume control, then 6Q7 triode grid, and so on like any old amp. Another pot either shunts highs from triode plate, or doesn't-shunt highs from volume pot tap. OT is on speaker *and* that connector has *Wall Voltage* on it!! (so it can't be run with speaker disconnected.)

[kagliostro]

A model that can be a bit similar is the G901



but only a bit

---

A friend told me that may be it was a model build in Argentina and if so, it may not be on the Geloso Bulletins


---


If despite all you don't find the schematic, you can use the PT, OT and power tubes to build an amp (a 5e3 ??)

Franco