Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 3 Next   Go Down
  Print  
Author Topic: Help with R390A audio section  (Read 8302 times)
N3DT
Member

Posts: 522




Ignore
« on: January 21, 2013, 08:32:44 AM »

I have 2 - R390As.  One of the audio sections works pretty good, but the B+ is a bit high because of solid state rectifiers in the PS.  I've got the ripple down to less than .05VP-P on the output of the RF/IF B+ (229VDC instead of 205).  The audio B+ is less than .05VP-P on the cathode follower, and the B+ to the audio amps is around 2VP-P.

The second AF module is very high in voltage, like 50 VDC more and the ripple is way up on the RF/IF B+, the AF B+ is high in voltage, but ripple is same as other module except the regulated 105VDC is higher.  I've been through the resistance measurements comparing from module to module and they seem to be fairly consistent.  I just can't figure the second module having this high voltage and 2VP-P ripple on the RF/IF B+.

I switched tubes between the modules and it got rid of some motor boating on the higher voltage module, but the ripple and voltages are still the same.

I did remove the 30/45uF capacitors and replaced them with new ones, in one module I used 47uF throughout (the one with the higher voltage) could this be my voltage problem?  All the other .01uF, .033uF caps have been replaced with .047uF.

Ideas?  Especially the 304VDC on the RF/IF B+.  I'm checking both AF modules in the same R390A so the only difference is the audio module.
Logged
W9GB
Member

Posts: 2616




Ignore
« Reply #1 on: January 21, 2013, 08:47:29 AM »

When you did the solid-state conversion .....

Solid State: (optional, only if 26Z5W tubes not available)  Cover tube socket  with labels regarding solid state mod.  Use 3A, 1KV rectifier diodes.  One diode between pins 1 and 3 of socket XV801, connecting the cathode lead to pin 3.  Another diode is installed across the same pins on XV802.  This change is documented INCORRECTLY in Navships 0967-063-2110, where it describes using pins 1 and 4.

Many suggest adding a 220 ohm dropping resistor to lower the B+ voltage to 240 VDC.  
(Also see HSN reprints, page 5)  
Some versions add the dropping resistor to the Power Supply Chassis with the 220 ohm 10 watt resistor between T801-6 and ground (http://www.qsl.net/wb4tur/milt/index2.htm website and in HSN issue 48, pages 5 & 6).  
Some add the 220 ohm resistor to the AF deck (Navy EIB 895 and HSN issue 2, page 5 or HSN reprints, page 5).  
I prefer to add it to the power supply deck so that I can freely swap power supplies between tube and solid state type and the mod travels with it.
==
Have you checked the value of R614 ?? (R614 560 ohm 1 watt resistor).

Chuck Rippel notes that this resistor can change in value,
 he replaces (when defective/out of spec) R614 with a 560 ohm 2 watt resistor.
« Last Edit: January 21, 2013, 09:00:37 AM by W9GB » Logged
N3DT
Member

Posts: 522




Ignore
« Reply #2 on: January 21, 2013, 10:30:59 AM »

I've read through all the mod recommendations at the R390A site.

The PS rectifiers were replaced when I got them.  One is with 1N561s and the other is with RGP30M (1000V 3A) I replaced because the job done was so sloppily.  I do still have two 26Z5 I could replace in one.  The sockets have been removed in the other one.  I looked for a 200-220 ohm 14W resistor, but couldn't find one easily, so that is not done.  I have installed the CL-90's in the one I'm playing with right now.

I could re-install the tubes and use that PS until I find some 220ohm 14W resistors.

R614 (560) measures 591 in the better module and 555 in the funky module, both within 10%.  They are both 2W and the funky module is with a new metal oxide 2W resistor because it was missing.  I still have another.

I'm wondering if using 47uF caps in place of the 30uF has increased the voltages in that module?
Logged
KD0REQ
Member

Posts: 897




Ignore
« Reply #3 on: January 21, 2013, 10:35:02 AM »

common electrolytic capacitor ratings back in the day were - 50% + 100%, so I'd look elsewhere for your higher B+ cause.  might you have a tube not drawing current, or a shorted-low resistor in the circuit path?
Logged
KE3WD
Member

Posts: 5694




Ignore
« Reply #4 on: January 21, 2013, 10:35:56 AM »


I'm wondering if using 47uF caps in place of the 30uF has increased the voltages in that module?

Very doubtful, impact should be minimal.  Check out the tolerances for electrolytics, for one thing.  

The dropping resistor is needed item.  

The R390A may have other problems, the incomplete solid state rectifier mod may be getting in the way of troubleshooting that.  

Since you have the tube and don't have the resistor for the solid state mod, why not implement the tube properly - and then check operation.  Even if you still have troubles in the AF section, you've eliminated the mod from the list of question marks and can then proceed to troubleshoot the AF problem.  


73
Logged
N3DT
Member

Posts: 522




Ignore
« Reply #5 on: January 21, 2013, 01:53:50 PM »

OK, I'm going to put the rectifier tubes back in the PS module that has the sockets and get into the AF modules with some more regular voltages.  I measured the new caps I got and they're pretty close to their given value.  Even the old ones were pretty close, but I replaced them anyhow.  I soldered the new ones in the bottom of the module to the octal sockets and just removed the old plug in ones.  Nothing is not reversible.



I've been through the PS circuit on the AF board including L601, L602, L603, and the large resistors R617, 618, and 619 and the only thing different in the 2 modules is the resistance of the chokes and that's not hugely different, but somewhat, maybe I should write it down to compare if someone else can give me values.
Logged
N3DT
Member

Posts: 522




Ignore
« Reply #6 on: January 21, 2013, 02:31:42 PM »

Before I remove the solid state rectifiers, I measured L601, 2, 3.  L601 is 109 ohms on the lower voltage one, and 66 ohms on the higher voltage one.  I wonder if anyone can measure their L601 for me to compare.  I'm wondering if the higher voltage one has some shorted turns.  Not sure how I would measure the henerys.  I'm sure that if that were the case, the ripple would be more, 20VP-P vs 3VP-P?
Logged
KE3WD
Member

Posts: 5694




Ignore
« Reply #7 on: January 21, 2013, 03:05:17 PM »

Let's find out exactly how much ripple you have and where the ripple is coming from.

Set your DMM (or VTVM) up for measuring AC volts and, starting at the filter cap that is last in the DC chain, find out what the reading in AC is there. 

Do the same for any supply voltages that are DC, right at the stage where you suspect a problem, I think in this case, the AF section. 

Hum can sound like ripple, especially if said hum is being introduced at the high gain input to an Audio stage.  This could be due to lack of shielding somewhere, or in the case of the older point to point wired boat anchors, might be cause by a simple wire dressing issue.  For example, filament lines were often routed in certain ways, wires twisted to reduce electomagnetic AC fields from them, dressed well away from critical input points and wires. 

Does the ripple appear as hum at the speaker? 

If so, does that hum change gain when volume control is rotated? 

73
Logged
AC2EU
Member

Posts: 361


WWW

Ignore
« Reply #8 on: January 21, 2013, 05:04:30 PM »

You mentioned "motor boating" in you original post. That is usually oscillation set up due to poor B+ filtering between stages. This clue and the ripple problem,it points back to a bad filter cap in that circuit area. Maybe one of the new ones are bad  or perhaps you missed one?

I don't know jack about the 390 specifically, but electronics is electronics...
Logged

N3DT
Member

Posts: 522




Ignore
« Reply #9 on: January 21, 2013, 07:04:15 PM »

I haven't dug into it any more, except to measure the 2 AF modules with the tubes out.  Nothing else in the rest of the radio is changed.  The voltage on the module with the 66 ohm L601 choke gives me 20VP-P ripple on my old Tec 545A scope.  Same location on the other AF module gives me 3VP-P.  This is at the input to the L601 choke right out of the rectifiers.  Like I say, same transformer, rectifier, different AF module which includes the power supply chokes and caps.  The new caps measure just fine on the Fluke 189.  The output of the high voltage module has 2VP-P out of L601, output of the better AF module L601 has less than 0.05VP-P ripple.  Actually neither module has much hum to it, that's not my issue.  That's more a function of the separate AF B+ which seems to be about the same in both modules.

To re-iterate:
Module #3267 at input of L601 = 3VP-P ripple @ 241VDC
Module #3267 at output of L602 = <0.05VP-P ripple @ 229VDC

Module #123 at input of L601 = 20VP-P ripple @ 315VDC
Module #123 at output of L602 = 2VP-P ripple @ 304VDC

Pretty much the same taking the tubes out of the AF modules.

My big problem is the 315VDC at the output of the rectifiers (input of L601) on module #123 and only 241VDC on the other one.  Only difference I can see is the L601 ohms, 66 on #123 vs 109 on #3267?
Logged
AC2EU
Member

Posts: 361


WWW

Ignore
« Reply #10 on: January 21, 2013, 07:42:43 PM »

Quote
My big problem is the 315VDC at the output of the rectifiers (input of L601) on module #123 and only 241VDC on the other one.  Only difference I can see is the L601 ohms, 66 on #123 vs 109 on #3267?

Is that "in circuit" or "out of circuit" ohm tests?
If that is out of circuit, then that is quite a difference for what should be the same part. "In circuit" tests would be useless, though .

Also, I'm still not sure what you are fixing. Is it just the voltage/ripple that bothers you or are there other symptoms?
I generally go by the circuit function tracing with a schematic rather than comparative analysis which can lead to incorrect conclusions.
Without some idea of the actual circuit, and no 390 experience to draw from, I am at a disadvantage.

Logged

N3DT
Member

Posts: 522




Ignore
« Reply #11 on: January 22, 2013, 06:34:20 AM »

My measurements of the input choke is 'in circuit', however the module is out of the receiver, so the input is not connected to the diodes and the output is not connected to the load, so there should be no problem measuring it in place.

What I'm trying to fix is the 20VP-P swing and the 2VP-P output on the first choke, plus get the DCV down to a reasonable value, 304VDC vs. the nominal 205VDC which is should be is way too much.  I realize some of it is removing the tube rectifiers and replacing with solid state, but if I could get the high voltage module in line with the other one I'd be happy.

I realized I have an old Heathkit Impedance Bridge.  I'll see if I can check the chokes with that, even if I have to remove them.  Other thing I can do as long as I remove the chokes is switch them and see what happens.  That's all I can figure since everything else checks out.
Logged
AC2EU
Member

Posts: 361


WWW

Ignore
« Reply #12 on: January 22, 2013, 07:37:45 AM »

Quote
My measurements of the input choke is 'in circuit', however the module is out of the receiver, so the input is not connected to the diodes and the output is not connected to the load, so there should be no problem measuring it in place.

Are you absolutely sure that there is nothing connected to one end of the choke? One thing I have learned overs the years is to ASSUME NOTHING!

Tube rectifiers typically gave a drop of 40 volts,as opposed to a silicon drop of .6v, so that's where the bulk of your voltage increase is coming from.
Perhaps you have leaky, but not completely bad solid state rectifiers? It happens...
If one choke is half the resistance of the other "out of circuit", then that is not a good sign. Some variance can be expected ,but not that much.
Logged

N3DT
Member

Posts: 522




Ignore
« Reply #13 on: January 23, 2013, 08:22:03 AM »

I've been playing with these 2 audio modules and the best one still has some slight hum to it.  The other one needs some tubes which I have, but I still have very high P-P voltage on the output of the rectifier, even with the rectifier tubes.  The tubes dropped the DC voltage about 20V.  Only thing I can figure is some of the chokes are bad.  I may try replacing the best ones into the good module.  I'm not going to destroy it, and chokes are rather expensive, if available at all, so my thinking is I'm just going to remove the tubes from the audio sections and install a LM380 type audio chip and rectify the 6.3 for the filaments to supply the chip.  But I'm not going to make anything non-reversible in case someone wants to put it back in original configuration.  It's just not worth it for me to spend that kind of money on this thing as long as I can get the RF and IF sections working good.

As far as the IF/RF B+ chokes I may see what I can do with another type filter, or I may spring for a new after market choke for the one that's bad.

I did try to measure the Henrys with the Impedance Bridge, but it didn't report very good results, much less than 10 Henrys and one is supposed to be 6 and the other is 2.5-12.5H, but then I was feeding them 1000Hz, not 60Hz and the reactance at 1000 could be way off.  The bridge did seem to measure capacitance pretty good.  I can feed the bridge with an external generator and I may try that.

I'm going to post a new thread to see what I should be seeing as far as P-P ripple on the outputs of the power supply.  I haven't seen that listed anywhere that I can remember.
Logged
AC2EU
Member

Posts: 361


WWW

Ignore
« Reply #14 on: January 23, 2013, 09:07:42 AM »

One of the things you can try is doing comparative ring testing between  the known good choke and the suspect one.
Bad inductors ring much less (or not all) than good inductors. With something that large you would need a low frequency fast rise time square wave pulse 20 -120 hz I suppose. The pulse excursion from high to low and low to high will cause a damped oscillation.

You can probably google "inductor ring testing" to see how to set it up.
You can also calculate the inductance with a LF sine wave into a LR configuration. XL=R at the -3db point which is .707 Vin.
Logged

Pages: [1] 2 3 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!