The AM Forum
March 28, 2024, 09:40:16 AM *
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: high voltage on Heathkit Apache TX-1  (Read 15035 times)
0 Members and 1 Guest are viewing this topic.
k3pf
Member

Offline Offline

Posts: 19


« on: December 19, 2014, 09:48:56 PM »

I recently acquired an Apache TX-1 and have gone through changing all the electrolytics and fixing up other problems to make it work.  The transmitter appears to work FB.  However, I am concerned about the high voltage I read on both my Apache voltmeter and also on my DVM.  The two readings are close to each other within a few volts, so I think the meters are reading the true voltage from the Apache's high voltage power supply (maybe).  When connected directly to the AC mains, I see about 890VDC on the Apache meter.  This is with no load on the high voltage supply.  That is , the transmitter is not tuned to put out any power.  I have not tried loading the transmitter up at this point so I don't know what the voltage will be when it is tuned up for 80-100 watts out.

My question are...
Is this voltage too high?  Should I be using a variac to keep the high voltage down?  I prefer not to use a variac if there is no problem because the variac is simply another external device that needs adjusting and I find that to be a nuisance.

Another concern is the that there may be way too much voltage applied to the EL-34 plates since that voltage is way high, too.  My concern stems from an article on wirelessgirl.com that says the high volts on the modulator tubes sometimes causes and arc between the plate pin 4 and the screen pin three due to the tubes being fed too much high voltage.

I would like to hear from those who have faced these or similar issues and whether I should truly be concerned about the high voltages I see.

Your responses will be greatly appreciated.  My only other tube transmitters were an ARC-5 and a DX-60 I used on CW as a Novice.  Therefore, my experience with tube transmitters is somewhat limited.
Logged
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 8154


CQ CQ CONTEST


WWW
« Reply #1 on: December 19, 2014, 09:54:25 PM »

My static HV on my Apache is about 900 volts. Both my HV anf LV supplies are solid state. Been that way since the 70's. Haven't seen any smoke rise from the Apache yet. When I transmit, it drops to around 800 volts.
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
k3pf
Member

Offline Offline

Posts: 19


« Reply #2 on: December 19, 2014, 10:19:50 PM »

Gee.  Thanks for the fast reply.  Makes me feel a lot better about the high volts.  I did expect the volts to drop under load and your loaded volts reading gives me something to look for.  I still appreciate further responses from other users so I can have more comparisons.

I checked my line voltage AC reading and it shows about 129VAC.  No wonder I see such a high voltage from the Apache.  I thought the line voltage should be no more than about 120VAC, not that it would matter all that much.  Go figure.

 
Logged
KB2WIG
Contributing
Member
*
Offline Offline

Posts: 4484



« Reply #3 on: December 19, 2014, 11:14:58 PM »


DVMs have a nasty habit of dying when the V gets up a bit. The ckt boards don't like HV. I'd consider not using the DVM to measure HV. Or better yet, get a HV probe with appropriate dropping resistance. 

 If you'r on a budget, get something like a Simpson 260, or a heathkit  VTVM ( like around $20) or an RCA 'Seniour Volt Ohmist. I've got a HP that's the size of a desktop computer, that I'd use for precision work. The $10 Heathkit VTVM is on the bench, and going strong.



klc
Logged

What? Me worry?
K9DXL
Member

Offline Offline

Posts: 150


« Reply #4 on: December 19, 2014, 11:37:39 PM »

Since your line voltage at the plug is about 129 VAC, you might want to see what voltage you have on your tube filaments.  You might consider using a variac or bucking transformer to lower the voltage a bit and prolong the life of the tubes.
Logged

Breathing solder fumes since 1959.  That explains a lot.
k3pf
Member

Offline Offline

Posts: 19


« Reply #5 on: December 20, 2014, 12:21:48 AM »

Thanks for the excellent replies.

My Simpson 260 died a slow death a long time ago and it has been replaced with a Radio Shack VOM.  Not the best for sure but it does agree within a couple volts or so with my Simpson DVM.  May not be the best but its all I presently own.

I checked the filament volts with my RS "VOM" at 6.5VAC (no transmit mode) and 6.4VAC in the full power 100W transmit mode.  On the other hand, the Simpson DVM shows 6.85 no transmit mode and 6.74 in transmit mode.  My guess is its not enough to be too concerned about since there should be no more than several milliamps more than the nominal 6.3V heater volts would draw.  Do you tube experts agree with my guess?

 
Logged
k3pf
Member

Offline Offline

Posts: 19


« Reply #6 on: December 20, 2014, 12:42:43 AM »

One other thing.  I checked the HV reading on the Apache with it transmitting into a dummy load at 100W.  The high voltage dropped down to about 780VDC which is in line with the 800V reading WA2CWA said he gets with his Apache (See his post above).  He said his transmitter has worked OK since about 1970, so I think I should be good to go once I get the VFO calibrated and get some sort of transmit receive switching arrangement wired up.  I used a simple relay for that purposed years ago when I was a Novice operator.  I suppose that should work OK for AM operation since there is no VOX to be concerned about. 
Logged
WQ9E
Member

Offline Offline

Posts: 3282



« Reply #7 on: December 20, 2014, 10:26:32 AM »

The no load high voltage isn't a problem but if your line voltage is truly 129 volts you should buck it down not only for the filament life but more importantly many vintage transformers approach saturation and run MUCH hotter with high line voltage.

Also carefully check and clean the 5R4 tube bases and sockets, these tubes are very prone to developing carbon tracks when used in transmitters.

Read the TX-1 manual carefully, particularly the part about adjusting the audio level setting through the CW key jack.  If this isn't set properly and you try to increase mic gain with the front panel control you will end up with heavy clipping and the oft discussed scratchy Apache sound.  And if you feel a compelling need to butcher the Apache with modifications at least make sure the basic transmitter is first operating properly and reliably.
Logged

Rodger WQ9E
Jim, W5JO
Member

Offline Offline

Posts: 2506


« Reply #8 on: December 20, 2014, 11:36:35 AM »

I checked my line voltage AC reading and it shows about 129VAC.  

Are you certain of the calibration of the meter you use?  That sounds a bit high but can be depending on where you are in the AC feed system.  If you do have 129 volts then you might want to call your supplier and have them verify.  Most of not all try to maintain 125 volts at the input to your home.
Logged
flintstone mop
Contributing
Member
*
Offline Offline

Posts: 5055


« Reply #9 on: December 20, 2014, 02:24:50 PM »


DVMs have a nasty habit of dying when the V gets up a bit. The ckt boards don't like HV. I'd consider not using the DVM to measure HV. Or better yet, get a HV probe with appropriate dropping resistance. 

 If you'r on a budget, get something like a Simpson 260, or a heathkit  VTVM ( like around $20) or an RCA 'Seniour Volt Ohmist. I've got a HP that's the size of a desktop computer, that I'd use for precision work. The $10 Heathkit VTVM is on the bench, and going strong.



klc

Yup
I Blowed out many a DVM's that claimed HV capable. You might be in dangerous territory passed 600VDC\
The Senior volt ohmist is the best, or a good ole Simpson.

Fred
Logged

Fred KC4MOP
k3pf
Member

Offline Offline

Posts: 19


« Reply #10 on: December 20, 2014, 03:18:04 PM »

All of your inputs about an incorrect DVM meter reading got me thinking that surely my Simpson DVM reading of 129VAC is probably not reading the proper line voltage into my home.  Therefore, I borrowed a couple of VOM's and another different DVM and measured the line volts again using those.  Unfortunately, none of these are precision instruments, either.  However, all three of these new meters show just under 125 VAC whereas my original Simpsom DVM still reads just above 129VAC.  Made me breath a sigh of relief knowing that.  Nevertheless, I really like the idea of using a buck transformer to lower the incoming voltage down to somewhere around 115VAC.  Are those transformers small enough to permanently mount one inside of the Apache?  I don't care much about using an external plug in device if its possible to make a permanent internal installation.
Logged
WD5JKO
Member

Offline Offline

Posts: 1996


WD5JKO


« Reply #11 on: December 20, 2014, 03:20:40 PM »


The Fluke 80K-6 High Voltage Probe is a good accessory for DVM's with a 10 meg input resistance, and female banana connection spaced 3/4".

These extend the range of the DVM to 6KV with a 1000:1 divider in the probe. So 890 volts would be 0.890 Volt read on the DVM

These can often be found used cheap. Amazon sells them new here:

http://www.amazon.com/Fluke-80K-6-High-Voltage-Probe/dp/B000LDCP4U/ref=sr_1_1?s=industrial&ie=UTF8&qid=1419106360&sr=1-1&keywords=fluke+6kv+probe#productDetails

Jim
WD5JKO
Logged
WD5JKO
Member

Offline Offline

Posts: 1996


WD5JKO


« Reply #12 on: December 20, 2014, 03:29:50 PM »

Are those transformers small enough to permanently mount one inside of the Apache?  I don't care much about using an external plug in device if its possible to make a permanent internal installation.

   A boost or buck transformer must be sized by the amount of voltage transformed times the amperes into the main power feed into the rig. So if your Apache needed 5 amps, and you wanted to buck the incoming voltage 10 volts, then you need a 10V @ 5A transformer with a 50VA rating. That would not bee too large.

  A better option is to throttle the incoming voltage to the shack to something that all your equipment can be happy with, like 120V...or even 115V for vintage gear. Some of the really old stuff, including some BA receivers, will overheat inside when the line exceeds a range anticipated by the OEM at the time of manufacture.

Jim
Wd5JKO
Logged
Jim, W5JO
Member

Offline Offline

Posts: 2506


« Reply #13 on: December 20, 2014, 04:08:54 PM »

However, all three of these new meters show just under 125 VAC whereas my original Simpsom DVM still reads just above 129VAC.  Made me breath a sigh of relief knowing that.

An old, old timer always said to verify your test equipment and cables before testing.  

As for your line voltage, it usually is specified at 125 (nominal) at +/- 10%.  So was your Apache.  Yes you will see slightly higher or lower voltages depending on the season of the year and time of day, but the Apache should be all right.  The fewer parts in the mix the better.
Logged
K4RT
Contributing
Member
*
Offline Offline

Posts: 520



« Reply #14 on: December 20, 2014, 04:12:14 PM »

I still appreciate further responses from other users so I can have more comparisons.

Checking my Apache notes, I recorded the HV under load on 5 DEC 2013 at 915 volts, and MV (point M in the schematic) at 396. I believe at that time I was powering the Apache with line voltage, which tends to hover around 121 VAC here.  I now power the transmitter using a Variac, with the output voltage set around 110 to 112 volts. The schematic is not at my fingertips at the moment, but I believe there is a notation on the schematic stating that the voltages noted were with the transmitter powered with 110 VAC. I would have to check the schematic to be sure, though.

With the Apache in stock configuration and the modulation and clipper set correctly, I received reports of good "communication" grade audio.  I later modified the speech amp circuit and removed the clipper.  The modulation appears clean on the scope, and I have received favorable reports.  However, I have not ruled out restoring the clipper at some point.
Logged
k3pf
Member

Offline Offline

Posts: 19


« Reply #15 on: December 20, 2014, 04:46:51 PM »

I just checked my downloaded assembly manual and it shows the input at 115VAC.  Assuming a 10% plus/minus variation, the line volts could increase by as much as 126.5VAC.  If my new readings of just under 125VAC is correct with the different meters I recently used to measure line volts, then everything should be OK without a buck transformer or variac although reducing the volts as some pointed out certainly is the safer bet.

I also checked the pins of the high voltages tubes as suggested and they looked clean.  However, I shot the sockets with some contact cleaner and wiped off the tube pins with cleaner and swabs as an insurance measure. 

Oh yea.  I want to point out that I do not want to make any major mods (butchering) that would destroy the original integrity of the original design.  I might change a few coupling capacitors that are supposed to improve the audio quality but that is a minor thing that can be easily undone if needed.

Hope to have everything up and running on the air within a few weeks or less.  Its been fun restoring this old tube set.  Thanks everyone for sharing all your ideas and tips.
Logged
Jim, W5JO
Member

Offline Offline

Posts: 2506


« Reply #16 on: December 20, 2014, 06:25:23 PM »

  I might change a few coupling capacitors that are supposed to improve the audio quality but that is a minor thing that can be easily undone if needed.

Parallel the coupling caps there.  That makes it easy to return to its original glory.
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8308



WWW
« Reply #17 on: December 20, 2014, 10:08:35 PM »

Back in the good old days you could get a Triplett VOM with a 5KV jack right on the front. That's what I'm talking about!  I have a fluke with 5KV probe, very nice indeed.
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
WQ9E
Member

Offline Offline

Posts: 3282



« Reply #18 on: December 20, 2014, 10:18:47 PM »

Patrick, I have a couple of the old meters with 5,000 volt jacks but I certainly wouldn't trust the leads for that voltage.  My large Tektronix scope probe is the only probe I feel comfortable hand holding near high voltage.  My Simpson DMM has a 5 Kv. multiplier probe that I clip in place before applying power.

Now this is a high voltage probe Smiley Tektronix P6015 good for 20 Kv. RMS / 40K kv. peak pulse but voltage ratings drop above 1 Mhz. down to around 4 Kv. at its maximum 75 Mhz. rating.


* P-6015 HV probe.jpg (115.74 KB, 800x534 - viewed 538 times.)
Logged

Rodger WQ9E
WZ5Q
Member

Offline Offline

Posts: 109



WWW
« Reply #19 on: December 21, 2014, 08:24:24 AM »

My large Tektronix scope probe is the only probe I feel comfortable hand holding near high voltage.  My Simpson DMM has a 5 Kv. multiplier probe that I clip in place before applying power.

Now this is a high voltage probe Smiley Tektronix P6015 good for 20 Kv. RMS / 40K kv. peak pulse but voltage ratings drop above 1 Mhz. down to around 4 Kv. at its maximum 75 Mhz. rating.


That's what I use, the Tektronix P6015 for the O'scopes, and the Simpson HV Test Probes for the meters.
The Freon level is still very good in my P6015 probe, although I have no more "spares".
Have you found a good alternative for the Fluorocarbon 114 since it is practically unobtainium now?
I have read that some people tryed using mineral oil but it requires a complete recalibration to use it.
Logged

Mike
WZ5Q
From Deep Down in the Dark Dismal Swamps of the Calcasieu
http://www.wz5q.net
WQ9E
Member

Offline Offline

Posts: 3282



« Reply #20 on: December 21, 2014, 08:39:21 AM »


That's what I use, the Tektronix P6015 for the O'scopes, and the Simpson HV Test Probes for the meters.
The Freon level is still very good in my P6015 probe, although I have no more "spares".
Have you found a good alternative for the Fluorocarbon 114 since it is practically unobtainium now?
I have read that some people tryed using mineral oil but it requires a complete recalibration to use it.

A friend at the university supplied me with a small bottle of 114 a few years ago so I am good for awhile but then I will have to search for something else also.  On one of the lists several years ago someone reported finding a supply while in Mexico but then you would have to smuggle it back across the border. 

After winter break is over I will check with a couple of profs I know in chemistry to see if they have any suggestions for a good replacement.
Logged

Rodger WQ9E
WZ5Q
Member

Offline Offline

Posts: 109



WWW
« Reply #21 on: December 21, 2014, 08:48:59 AM »

After winter break is over I will check with a couple of profs I know in chemistry to see if they have any suggestions for a good replacement.

Much appreciated Rodger.
I'll let you know if I gain some knowledge as well.
Logged

Mike
WZ5Q
From Deep Down in the Dark Dismal Swamps of the Calcasieu
http://www.wz5q.net
K4RT
Contributing
Member
*
Offline Offline

Posts: 520



« Reply #22 on: December 22, 2014, 03:41:34 PM »

I believe there is a notation on the schematic stating that the voltages noted were with the transmitter powered with 110 VAC. I would have to check the schematic to be sure, though.

I checked my copy of the TX-1 schematic, which notes "120" volts.
Logged
Jim, W5JO
Member

Offline Offline

Posts: 2506


« Reply #23 on: December 22, 2014, 05:28:50 PM »

I believe there is a notation on the schematic stating that the voltages noted were with the transmitter powered with 110 VAC. I would have to check the schematic to be sure, though.

I checked my copy of the TX-1 schematic, which notes "120" volts.

So 125 volts is not out of range.
Logged
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2648


Making AM GREAT Again!


« Reply #24 on: December 22, 2014, 09:56:33 PM »

  On one of the lists several years ago someone reported finding a supply while in Mexico but then you would have to smuggle it back across the border.


You mean,  like....   Walk.

The border is porous.   Just ask any of us who grew up there.

--Shane
KD6VXI
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 0.088 seconds with 19 queries.