Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
National R-175-a Cleanup results




 
The AM Forum
April 05, 2020, 07:00:48 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: National R-175-a Cleanup results  (Read 11413 times)
0 Members and 1 Guest are viewing this topic.
w1vtp
Member

Offline Offline

Posts: 2618



« on: September 27, 2009, 04:07:05 PM »

OK

Here's the results of the R-175-a cleanup.  I took the advise of using warm water and a soft toothbrush.  I apologize for not taking detail of the "bad side." In my excitement of a successful cleanup I forgot it.  However, you can see the results as the pictures show.

Thanks for the advise -- what water + packing material put on, warm water took it off.  I dried it off with my wife's hair drier afterwards.  The second R-175-a I bought from Fair Radio recently.  Right after I bought it, the ad took the listing off.  Must've bought the last one.

Al


* R-175-A_GOOD_SIDE_AFTER.jpg (984.72 KB, 1705x795 - viewed 404 times.)

* R-175A_BAD_SIDE_BEFORE(2).jpg (101.27 KB, 1303x1138 - viewed 442 times.)

* R-175-A TWINS.jpg (747.7 KB, 854x956 - viewed 529 times.)
Logged
N3DRB The Derb
Guest
« Reply #1 on: September 27, 2009, 07:44:25 PM »

al,

I have a pair of twins exactly like yours, except my used one is missing the little flared washer on top of the small insulator. My new one well, looks new, windings snow white. I guess heat turns the wire brown. I had never seen a brand new one before I got mine, and I had no idea that the windings are snow white on a new one. I thought they came brown colored. Cheesy

upon closer exam, it looks like some brownish colored coil dope was put on there.

The 175/a is a 800 ma job, the R152 (only good for 160 & 80 ) is 600, and the R154 80 40 20 10 is 600 too.
Logged
w1vtp
Member

Offline Offline

Posts: 2618



« Reply #2 on: September 27, 2009, 10:13:17 PM »

al,

I have a pair of twins exactly like yours, except my used one is missing the little flared washer on top of the small insulator. My new one well, looks new, windings snow white. I guess heat turns the wire brown. I had never seen a brand new one before I got mine, and I had no idea that the windings are snow white on a new one. I thought they came brown colored. Cheesy

upon closer exam, it looks like some brownish colored coil dope was put on there.

The 175/a is a 800 ma job, the R152 (only good for 60 & 80 ) is 600, and the R154 80 40 20 10 is 600 too.

Looks like we're headed down the same road in our XMTR projects.  Keep us all apprised on ur progress.  Got any details on ur mod design?

I've attached a design I plan to use that comes out of a Bill Orr Handbook.  I have all I need including either a UTC CG-59AX (20 watts) or a UTC S-19 30 watt modulation transformer (turn it around backwards for use as a driver).  My Mod iron is either a RCA 80 pounder or a UTC CM-4. Nice thing about this design is that it doesn't require any grid bias or screen supply voltage.  Fun eh?

Al

* w1vtp_modulator design.pdf (1543.08 KB - downloaded 220 times.)
Logged
N3DRB The Derb
Guest
« Reply #3 on: September 28, 2009, 03:44:15 AM »

yes it is. nothing like homebrew. you learn so much as you go. I never ever got the satisfaction I did from any other gear than I got from homebrew #1.

I am extremely interested in both of those circuits. especially the 803 one. I have a lot of 572b's that need to be used, provided I can get the stupid 2A3 6A3 6B4 6A5 driver tubes from someone. the 807 cathode follower is slick. I have a new 807 with a recessed special socket that needs to be used.

hmmm triode connected 4E27's??? would save a lot on vertical rack space is on a 3ft rack is rather important. I'm gonna use my R-175's on my 4-400 decks - use the new R-152's I got for the 4E27's.
Logged
N3DRB The Derb
Guest
« Reply #4 on: September 29, 2009, 04:58:06 AM »

hey Al,

can you tell me the value of the grid resistors he's talking about that the smaller tubes need but the larger ones dont?  may be using 807's triode connected as such for my 'low power modulator'. It needs to make 100 plus a bit watts of clean audio. 809's are what I really want, but they seem to be rather rare.
Logged
w1vtp
Member

Offline Offline

Posts: 2618



« Reply #5 on: September 29, 2009, 02:57:46 PM »

hey Al,

can you tell me the value of the grid resistors he's talking about that the smaller tubes need but the larger ones dont?  may be using 807's triode connected as such for my 'low power modulator'. It needs to make 100 plus a bit watts of clean audio. 809's are what I really want, but they seem to be rather rare.

Here's my preliminary answer.  This was taken out a 1947 RADIO HANDBOOK - pre-W6SAI.  I apologize for the poor image quality.  I can get a better copy to you if you're interested.  It looks like something in the vicinity of 470 ohms going to each 807 grid would be a good starting point.  Do you have a good power load that would simulate the final you want to modulate?  If so, you could scope the output before you actually put it on your RF deck. Lemme know if you are interested in a better copy -- I can snail mail it to you.

Note the novel way the 807's are driven.  Actually a variation of cathode follower is used using a 6SN7.  The resistive network could be replaced with a XFMR, but why bother.  The circuit is good as is.  Just fatten up the coupling caps for low end response. Again, I can send you the whole article - if you are interested.

Al

* 807 modulator.pdf (237.78 KB - downloaded 180 times.)
Logged
N3DRB The Derb
Guest
« Reply #6 on: September 29, 2009, 03:18:33 PM »

well, I'm following an existing physical layout that already has a driver transformer in there and the chassis cut out for it. So I'm sorta locked into building into a pre made layout. I did that because drillage and blastage of chassis is so hard on me. I'm just gonna build it for maximum tetrode scrote and VR tube the screens and use fixed bias. I am drilling the HV ceramic feed thru holes today, 4 of em. Gonna go ahead and lock down the mod transformer too. then it's a matter of wiring.

I'll upload some progress pix at the end o the day.  Cheesy
Logged
w8khk
Member

Online Online

Posts: 924


This ham got his ticket the old fashioned way.


WWW
« Reply #7 on: September 29, 2009, 03:54:04 PM »


Note the novel way the 807's are driven.  Actually a variation of cathode follower is used using a 6SN7.  The resistive network could be replaced with a XFMR, but why bother.  The circuit is good as is.  Just fatten up the coupling caps for low end response. Again, I can send you the whole article - if you are interested.

Al

Hi Al,

That is an interesting circuit, similar to the 6AS7/6080 cathode follower I used to drive the 4 push-pull parallel 1625s in my Valiant mods.  But there appears to be a serious problem with the bias on the 807s in the circuit as posted.  The way the VR-105 is wired, the cathodes of the 6SN7 would be positive well over 100 volts with respect to ground, and this is in turn direct-coupled to the 807 grids.  There is no cathode bias; the 807 cathodes are grounded.  This puts the 807s into saturation.....  Perhaps pin 2 of the power connector is a negative bias supply?  If that is the case, then the VR-105 is wired incorrectly.  But reversing the polarity of the VR-105 would upset the negative bias on the 6SN7 grids....   I would be very interested in seeing the entire article, as I do not have an older west-coast handbook than mid-50s.  My apologies if this is too far off the thread topic, we could discuss offline or in another thread.  Either scanned and emailed, or snail-mail would be good for the article, I am good in QRZ and my email is mycall at arrl dot net. 

Thanks!

Rick/W8KHK
Logged

Rick / W8KHK  ex WB2HKX, WB4GNR
w1vtp
Member

Offline Offline

Posts: 2618



« Reply #8 on: September 29, 2009, 05:07:23 PM »

Rick

You're right.  It is a bit off the thread but that's OK.  You point is taken on the issue with the bias circuit.  The bottom ends of R 19, 20 go to a -105 volt supply, so the text says that the net voltage is -30 volts on the 807 grids.  I'll post this as a novel approach to an 807 modulator and see what happens.  Thanks for the idea.  I can post the entire article at that time.  We could check with the author but I think he might be indisposed  Grin

Derb and I were talking about using a XFMR as a driver in the circuit and the subject of the resistor in the grid circuit came up - hence this diag...  Lemme put together things and post it and we can bang the idea around.  I think it's a novel way to drive the 807 modulators.

Regards, Al
Logged
w8khk
Member

Online Online

Posts: 924


This ham got his ticket the old fashioned way.


WWW
« Reply #9 on: September 29, 2009, 06:55:15 PM »

 You point is taken on the issue with the bias circuit.  The bottom ends of R 19, 20 go to a -105 volt supply, so the text says that the net voltage is -30 volts on the 807 grids.  

Thanks, Al.  I look forward to seeing the entire article.  Based upon your comment, it is obvious that the VR-105 needs to be installed opposite of how it is shown in the schematic, that is, ground the anode, and connect the junction of R-19, R-20 to the cathode.   On second look, the grid bias for the 6SN7 should be fine with this change.  

I believe the cathode follower will be much better than a driver transformer, and it will easily allow the 807s to run some grid current into AB2.  Not only do several high fidelity tube amplifiers use this technique, but also it is found in some broadcast transmitters.   For example, the RCA BTA-1M uses two 807s as a push pull gain stage, driving another pair of 807s as cathode followers, directly coupled to the grids of the 833A modulators.  Then they wrap a bit of feedback from the plates of the 833As back to the grids of the 807 gain stage.  In the RCA, and in my Valiant mods, the adjustable bias is applied to the grids of the cathode followers, thus setting the operating point for the cathode follower as well as the modulator stages.  In my modded Valiant, I went through several gyrations in choice of B+ and B- voltages for the cathode follower before I got a decent response curve from the modulators, but now I am able to get about 125 watts RMS from the 4 1625s into the UTC S21 mod tranny, with only 640 volts on the HV bus!  The audio is flat within 1db from 30hz to 14khz, and the lissajous pattern shows negligible phase shift throughout the range - so this method does indeed work!  By the way, I started out using a 6SN7 for the cf stage, but I was running very close to the dissipation rating on that tube.  Now I am running a 6AS7/6080, which has the same base pinout, lots more dissipation, albeit a bit more filament current.  Luckily I did not have to go to a 6336A!
Logged

Rick / W8KHK  ex WB2HKX, WB4GNR
w1vtp
Member

Offline Offline

Posts: 2618



« Reply #10 on: September 30, 2009, 03:02:50 PM »

Derb

Here's the missing info.  I was wrong.  470 ohms is not going to do it.  I'll let the article speak for itself.

Rick:

You're right on the VR tube.  There are enough problems with that whole article that I want to rework the whole thing.  Let's keep in touch

Al

* figure 17.pdf (775.7 KB - downloaded 200 times.)
Logged
N3DRB The Derb
Guest
« Reply #11 on: September 30, 2009, 06:21:21 PM »

Quote
into the UTC S21 mod tranny, with only 640 volts on the HV bus!  The audio is flat within 1db from 30hz to 14khz,

an S21 is capable of that kind of response? thats what I'm going to be using, but I'm just gonna go old school and use the S-9 driver. otherwise I'd have a gaping empty rectangular hole in my chassis.  Tongue
Logged
w8khk
Member

Online Online

Posts: 924


This ham got his ticket the old fashioned way.


WWW
« Reply #12 on: September 30, 2009, 07:28:41 PM »

an S21 is capable of that kind of response?

Yes, Derb, I finished the audio tests on my modded Valiant a couple weeks ago.  I used an HP audio generator and distortion analyzer, and a Tek 2247 scope.  I could not get near that response with a transformer driver, and I spent several months working on the phase splitter, gain stage, and cathode follower before it behaved properly.  Early testing indicated that I could not get the required power from a pair of tetrodes (either 807 or 6146) using the standard HV supply voltage (around 640 vdc).  Others have built strapping cap input supplies for the modder, and used the existing choke input PS for the class C final.  But I did not want to do this for fear of running such high voltage on the mod tranny, because I only have one and do not want to zorch it before the first YaaaLOW.  I decided to run four 1625s (12 volt, 7 pin 807s) in push pull parallel, lowering the output impedance, thus allowing enough plate current at 640vdc to produce 120 watts at lower voltage on the mod tranny.  I have not yet fired up the final - all testing was done with three 600 ohm 50 watt resistors in series, 1800 ohms which closely simulates the 1950 ohm load of the final running 300 ma at about 650 volts.  The impedance is slightly less running 333ma, but I do not really want to push it.

 Another thing that really helps is to use the modified heising to supply plate current to the final.  In my case, I used the original Valiant mod tranny, with all windings in series, and a microwave oil cap for blocking from the cold end of the mod tranny secondary to ground.  Getting the unbalanced dc current off the secondary of the tranny really enhances the low-end response.  I did some testing of the tranny using a resistive load fed with a variable dc supply, enough to put 250ma dc current through the secondary, and the bottom end fell off more than 3db at 250 Hz.

I attached an old photo of the modulator section of the Valiant, showing how I fit all the parts.  All the power supply and heising reactor parts are on the other side of the chassis.

By the way, my Valiant no longer has a mic input stage.  Just line level XLR connector from the audio chain feeding a UTC A-10 input transformer directly to the phase splitter stage.


* modulator_1.jpg (117.31 KB, 1024x768 - viewed 402 times.)
Logged

Rick / W8KHK  ex WB2HKX, WB4GNR
KM1H
Contributing
Member
*
Offline Offline

Posts: 3519



« Reply #13 on: October 01, 2009, 09:17:13 AM »

It would be a shame to waste those 2 chokes on anything less than a shunt fed PP 250TH amp Grin

Carl
KM1H
Logged
w1vtp
Member

Offline Offline

Posts: 2618



« Reply #14 on: October 01, 2009, 01:42:50 PM »

It would be a shame to waste those 2 chokes on anything less than a shunt fed PP 250TH amp Grin

Carl
KM1H

How about a pair of 304TLs Grin
Logged
w1vtp
Member

Offline Offline

Posts: 2618



« Reply #15 on: October 01, 2009, 02:04:16 PM »

an S21 is capable of that kind of response?

<SNIP>
By the way, my Valiant no longer has a mic input stage.  Just line level XLR connector from the audio chain feeding a UTC A-10 input transformer directly to the phase splitter stage.

Vy nice on the xfmr - Rich.  It looks similar to mine (see attachments).  Do you have the hookups for urs?  It might be the same as my HA-100

Al


* UTC_A10_INPUT_XFMR.jpg (72.99 KB, 1146x128 - viewed 376 times.)

* UTC_HA-100_CAT_LISTING.jpg (105.04 KB, 1124x172 - viewed 343 times.)

* UTC HA-100.jpg (96.09 KB, 1149x510 - viewed 406 times.)
Logged
w8khk
Member

Online Online

Posts: 924


This ham got his ticket the old fashioned way.


WWW
« Reply #16 on: October 01, 2009, 02:46:29 PM »

Do you have the hookups for urs?  It might be the same as my HA-100
Yes, the connection diagrams are the same for the A-10 and the HA-100.  I sent the relevant pages from the UTC book to your email, al at yourcall...  Attached is the underside view of the modded Valiant, still lots of wiring to do in this many-month-old photo.  Only thing left to fix is some bad relays.  Short on space under chassis, and I slobbered in some relays that were designed to be used in sockets, and I may have gotten to many calories on the pins, maybe melted them out of alignment.  Pain to replace, I wish I had used the sockets.  If it isn't one thing, its another!


* a10.jpg (237.76 KB, 1280x960 - viewed 419 times.)
Logged

Rick / W8KHK  ex WB2HKX, WB4GNR
KM1H
Contributing
Member
*
Offline Offline

Posts: 3519



« Reply #17 on: October 01, 2009, 08:49:17 PM »

Quote
It would be a shame to waste those 2 chokes on anything less than a shunt fed PP 250TH amp Grin

Carl
KM1H

How about a pair of 304TLs Grin
[/quote]

I use those as modulators for the 250TH's.

Carl
KM1H


* 304tl.jpg (206.62 KB, 700x474 - viewed 476 times.)
Logged
N3DRB The Derb
Guest
« Reply #18 on: October 01, 2009, 09:46:12 PM »

how much filament power those twins take? A damn lot I know.

Logged
w8khk
Member

Online Online

Posts: 924


This ham got his ticket the old fashioned way.


WWW
« Reply #19 on: October 01, 2009, 09:52:35 PM »

how much filament power those twins take? A damn lot I know.

A pair of 304TLs -  50 amps at 5 volts.  Keeps the shack cozy and warm in the winter!
Logged

Rick / W8KHK  ex WB2HKX, WB4GNR
N3DRB The Derb
Guest
« Reply #20 on: October 02, 2009, 07:08:28 AM »

and here i thought my fil unit for 2 4-400's was heavy. ( well, it still is )  Tongue
Logged
The Slab Bacon
Member

Offline Offline

Posts: 3934



« Reply #21 on: October 02, 2009, 07:47:51 AM »

A 304TL is actually 4 75TLs in one one bottle. (or 2 152TLs)
Logged

"No is not an answer and failure is not an option!"
KM1H
Contributing
Member
*
Offline Offline

Posts: 3519



« Reply #22 on: October 02, 2009, 10:51:46 AM »

Yep, it has a split filament so either 5 or 10V can be used. I run mine at 9.5V using a Variac and some oddball 11.5V iron I had on hand. That very high emission reserve (it was designed as a radar pulse tube) is why it works so well as a modulator with very low distortion, even with highly processed drive.

Carl
KM1H
Logged
The Slab Bacon
Member

Offline Offline

Posts: 3934



« Reply #23 on: October 02, 2009, 01:39:27 PM »

It ia also one of the very few triodes that will operate in AB1 as well as Class B & C
Logged

"No is not an answer and failure is not an option!"
KM1H
Contributing
Member
*
Offline Offline

Posts: 3519



« Reply #24 on: October 02, 2009, 08:56:37 PM »

Only problem with AB1 on that tube as modulators is low output. Less than 700W at 3kv Grin

Im running about halfway into AB2 and a good 1200W real world capability at 2500V. That gives me plenty of audio for 1400W input of the 250TH's plus plenty of reserve.

Carl
KM1H
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.079 seconds with 19 queries.