The AM Forum

After my 300 is on for several hours and I have used it for at least an hour.. The T2 high voltage transformer in the rig starts buzzing LOUD.  Its a high pitched solid and steady BUZZ noise out of the transformer itself. The radio has full power, audio and the noise is NOT on the air. Grid drive and FREQ are all stable and normal. But the noise is very loud in the room.  There is no drop in plate current or wattage at all.

Should I expect this transformer to die soon?  Any ideas on what to check or things to do?

Any sources for a replacement or ideas on what transformer will work in its place if it needs to be replaced?

On the schematic it simply takes line voltage to 1000 volts AC to the 866s.  This radio loads at 330MA but I never load it past 265.  Output power is about 150 watts AM.

I really enjoy this transmitter.. It happened tonight as I was talking to K4KYV DON on 3885.. It just all of the sudden goes into a loud BUZZ.

Clark
ke7trp

sounds like you have some loose laminations in the core. Check to see if the screws that hold it together are still tight. The renewed heating / cooling cycles may have worked them loose.

also check your HV filter choke. Choke input power supplies tend to really work the laminations in the filter choke.

                                                  the Slab Bacon

Clark, I have a Chump 350. I lost T-1 the LVPS just by basically turning it on and letting it 'warm-up,' (standard procedure for the AX9909's). Anyway, it warmed up too much and released it smoke. The lesson here is never turn your back on a rig. WRL was not know for using A-1 quality parts. Your milage may vary.

Clark,

As Derb identified the noise is almost surely from loose laminations but you need to see if this is due to normal temperature rise loosening the structure of if something is causing your current draw to increase in mid transmission leading to the buzz.  If you have a clamp type AC ammeter you could arrange this to see whether the primary current draw goes up simultaneously with the buzz and if so then you need to find out what is causing the additional draw.  If it remains stable then stabilizing your core is all that is needed.

As to the 866 rectifiers; they are pretty but I personally wouldn't keep them with any transformer that is expensive or difficult to replace.  One good flashover and it's bye bye transformer.

Sometimes the cabinet will vibrate and make that noise if the transformer is moving slightly.  Are you sure it is the transformer?  Check it like Rodger said and if the transformer is ok then you could mount it on rubber grommets to help that.  Check to see if the screws holding it together are tight, and if that doesn't do it, the bobbin in the transformer may be moving a bit.  You can pull off one of the end bells and use a piece of a tooth pick to wedge it still.

As Mike explained that LV transformer is usually a the real problem with these things, so watch it.  Check the leakage on that 3X10uf can cap in the audio section for leakage.  If it is excessive, replace it.

Clark

All suggestions here are excellent so far so I'm just going to repeat things.

I'm thinking loose laminations.  I had the same problem with my old Eldico TR-1 many years ago <sigh>.  Had you taken HV PS voltages in the past and documented it?  How does the present HV compare.  Is the ripple still  OK (on air reposts should verify this). 

Another idea is this:  given the high frequency component of what you hear, check your cabinet, chassis bolting to rack etc.  I have an EF Johnson Courier that works just fine but once in a while it does that hum/rattle thing.

It's a good idea to CAREFULLY check HV, ripple HV resting current draw when the XMTR is working OK so that if the beastie starts to act up you have a snapshot of what it was like when it was working OK.

73, es GL, Al

Thanks alot guys..  This is a real loud buzz.  Its so loud you are waiting for it to go bang and see smoke.

All the caps in the radio are new except the old oil can Sangamo Cap.  Its not leaking.  Since I stare at the plate meter when I talk on it, I know its not going up or down in current.

I have isolated this to be the T2.. in my mind is this:

If I turn the Rig to the TUNE postion, I get NO noise at all.. and about 20 watts out. Not a single buzz or noise.. If I go to CW or PHONE, I get the loud BUZZ and 150 watts out. In my mind, I figured this would mean its the HV transformer. The sound sure seems to come from the big transformer in the back left. 

I will have to tear it down AGAIN and make sure the T2 is tight. I was used this rig for 7 months with out issue. Then one day, The BUZZ came on during a QSO.  I have faught with it to fix it. I hope its just the Loose core that I can tighten. It sure has full power and works perfectly. So whatever it is, Its not effecting performance or sound on the air.

This radio also has no hum.  I just recently replaced all the caps in the audio section with new 22 UF caps. No more papers are left in the rig. As I replaced them, I turned it on and listened on a RXer. My hum was gone when I got the last Cap replaced.

The BUZZ also varies GREATLY as I dip the plate.. Increase load from 250 to 300 MA and the noise doubles in volume.

Clark

I forgot to add...

I am using the big plug in replacement diodes for the 866s..  The 866s have been out for 8 months.

On the LV side it has the original 5u4G installed. I just looked through the case and noticed the getter is burned off it..  Maybe I should start by replacing the 5U4?  I have a plug in replacement diode and I think I might have at least one 5U4G somewhere.

Clark

Clark,

I don't have the schematic of your transmitter handy but there are numerous sources of current draw that will not show up on the plate meter.  For example, increased current draw due to problems with the rectifiers or filters won't show up on a plate meter that reads final cathode current.

Here is the schematic.  and voltages.

Clark

I am curious Clark, you say you are only loading the plate meter to near 265 mils?  The book on this thing says never go below 275 due to the reflected impedance to the modulation transformer.  Does the buzz change if you load it heaver?

If I load this thing to 300 or 330 then you get back swing on the plate meter when you modulate. Its a 200 watt carrier which is a hell of alot for these tubes.

I can try to load it up higher...

Clark

Clark said:
You mind those AX9909's. They are like hen's teeth to find. Unless you want to modify it for a suitable replacement knock yourself out. But treat those finals like VIPs if you want prolonged service from them.

That is why I tend to load it on the light side.  It makes an easy 150 watts out at 250 to 275 MA.  If I load it up to 300+ it goes near 200 out and its just to much for the entire rig.

Clark

Working on the 300 now trying to get it up for the wed night AMI net on 3870.   

Loading to 330 MA just as the manual suggests makes 200 watts out on the 500 slug and the 1000 slug.  Buzz is less... Still there.

A carefull listening and I think its actualy from the transformer in front of the big one. THe LV unit. I tested out a Pwd plug in replacement for the 5U4 and the buzz is nearly gone.... I wonder why. I thought this would have been harder on the radio.

With the unit 1 inch out of the case, the noise is low... What I would call normal.. If I slide it all the way in and bolt the case back down its LOUD.. So the case is transmitting the noise like a speaker cone.

Clark

I hacked up a plastic coat hanger and used it to hold to my ear to find the source of the noise.

Its the BIG HV transformer. NOT the small one.

When I held the plastic rod at the transformer and then to my ear while keyed, Its Super loud. A neat way to find noise like this. Obviously, Be carefull!!!
This plastic rod was a foot long at least.

I have tried:

866a's
3b28s
Plug in diodes.

ALL have the noise.. Full power out. That thing does 200 watts with 120 % mod... Its always been super strong.

The buzz is so loud that I cant use the radio. Its as loud as someone talking to you in the room. I tightened the mounts SUPER tight and wrenched the plates down hard. No change. I guess its toast or about to be toast.  At any rate, I cant use the radio like this. It ran noiseless for 7 months and then all of the sudden the noise came in LOUD during a QSO.

Any ideas on a transformer that would supply the volts and amps needed?  Its 1000VAC. The plate current is 330 MA.

I guess its back to the 40 watt ranger :(   Thanks alot for all of the help guys!!!! 

Clark

I got mine off of Bob, W2ZM. I'm not sure if he modified it or if someone else did but there seemed to be gobs of black RTV at the feet of the HV transformer. When mine was working, I never noticed a buzz.

Mine buzzs some but not REAL loud.  It is enough for the buzz to be heard over the air if I set the mic right in front of the transmitter.

On that downward modulation, mine will do the same if I am not careful in tune up.  Verify the shunts are correct if you can measure them.  I am going to give some advice my old elmer told me years ago and is still printed in some books.  First load the transmitter to max power out at or below the suggested plate current.  Mine has 200 + watts out near 300 ma.  with grid drive set at 10 ma. The last thing is to be sure the plate cap is at the dip, and I am assuming you have neutralized the final.


Once you have it loaded increase the grid drive until power out doesn't increase, then back grid drive off until you have a grid reading that keeps the power output at the max level.

You should also keep the audio set  to produce peaks just below the 200 ma mark on your meter.  If you drive it too hard, it will cause the plate reading to decrease markedly.

Hey Jim.. sell me your champ.. I'm tired of being PW... How you and the misses doing.. recovered from the twister i hope.

We are fine here Jerry.  That tornado passed 3 miles South of us and lifted just South of the house.  I have been picking up debris all over the 2.5 acres.  Everything from fiberglass insulation pieces to a large pieces of twisted 26 gauge metal from the roof of something.

I have to hang on to the Champ right now.  It is the only table top transmitter I have.  I have it and the GK 500A but the 500 is hardly a table top.  With some work like Clark is doing, they are good transmitters.  Simple, straightforward and plenty of power for it's size. 

If you run int one let me know... I gota get more scroteful...

I'm wondering if we can veer off and consider removing the transformer, removing the bells if any, exposing the laminations and heating up the core to 150 degrees in the oven than soaking the thing with varnish? Just thinking of  things I would try. If it's making a noise due to loose iron I would think that would help. Leave it outside until it's tacky and stops dripping then put it back in the oven. Open the windows to let the smell out and after a couple of hours maybe you killed the noise? Any more bright ideas?
Keith
WA1HZK

Keith that would probably work, but I would probably just remove one of the end bells and put something that won't arc between the bobbin and the laminations.  Try to immoblize it and the noise may go away. 

Just sitting here, I am trying to think of some form of caulk that will work, maybe Gary will chime in here and give some good directions.

I often wondered if it is worth trying a can of foam insulation. Spray in the gaps with the liquid then it expands into a strong foam. It costs $5 at home cheapo

I as on the on the AMI net and the thing got even worse Now the power is down. I turned it off and I had to go to a rice box!

I am going to work on it today guys. I wonder the relay has died again.

Clark

Spent some time with the 300 today since the 500C is now up and running :)

One of the HV power chokes was the culpret of all my trouble. Its fixed now. I also isolated the chokes with Rubber Vac line.  Oiled and tightened the fan and cleaned the Changover relay. 

Now I am back at Full power and when you key it, all you hear is the relay clicking.. No buzz at all and no chassis hum ect.. 

Going to install it back in the main operating position tomorrow and take the 500c down for upgrades. Good to have my old pal the Globe Champion 300 back!

Thanks to all for the help!

Clark

I always thought the chumps were neat transmitters, they look nice, compact package, but every one I heard of blew up, odd hard to get tubes, etc.
There cant be many of them left working...

Brett

Thats very odd you say that :)   You must be thinking of a different transmitter?  Its not compact by any means. Its nearly twice the size the valiant :)  Its a Brute and way over built in most areas. Its also around 130 lbs so about half again the weight of the valiant.

 I know of 4 or 5 running now.  Mine ran for nearly a year before needing service.  I think the reason we dont see more of them is simply because they where expensive and WRL just did not sell as many in comparison to the the Johnsons and others.

Clark

My 300 has been reliable and runs just fine, although I haven't had it on air for a couple of years.  Had a 350 in High School (early 60's) paired with an RME 4350A, and bought this 300 in the mid 1990's to relive the glory days .. or something like that :-)

I'm fortunate to have a couple of sets of NIB AX9909s in case the (still) original pair decide to give up the ghost.  I have an extra shield bracket that I planned to cut holes in to mount cooling fans (a la the 300A), but that project keeps falling to the bottom of the list and more than 10 years later hasn't happened yet .... but there's always tomorrow.

Typical of the 500 series, mine is finickey about loading on 75 and 160.  I use a tuner after it and it just plays fine.  Have been using it regularly for 3 years now and it does not have a problem one.

To cure the 300 ohm impedance problem on 160, I changed the bandswitch to one out of a DX 100, added an L coil and changed the load cap to one that has 450 pf.  I now loads into 50 ohms on 160 fine.

They are physically about the size of a DX 100.  They are shorter and a bit deeper but the width is the same.  Weight is about the same as well.  According to the book it is 105.  I did change the finals to 8643s to get away from the AX 9909s and sold them.  Has the same power out and sounds as good as a stock champ can.

MIne makes decent power on 160. About 140 watts with 100%. I never bothered to mod it. On 75 it will do 175 easy. I run it about 150 most of the time on 40, 75 and 160. I band change it daily. Mine is alot heavier then 105. Who knows. Maybe they used different Iron in mine. Its an early one. My 9909s are strong. I have a spare set of Tungsrams off ebay. They load to no more then 100 watts. They work great but just have less power then the Amprex.

My Champion has Roberts Audio modifications done. Its a simple kit that he sends you with a schematic. Its not expensive and he includes all the parts so you dont have to go around searching for the right caps and resistors.

This mod matches the D104 to the Radio properly, then bypasses the Speech filter and runs the audio straight. With a Stock D104 mic, the audio is just fantastic. People listened to me for 6 months on the stock setup and then heard me on the modified version and flat out loved it. This mod is reversable and no parts are removed.

Highly recomend the W0VMC kit.

I will be on the AMI net tonight on 3870 around 7 to 8 pm. Then hanging out for the round table with my 300 of anyone wants to hear it!

Clark

I know gk changed models over time, but I remember one I looked at 25 years ago, being about the size of a dx100. With dx100 size parts...

Really small for the power rating...maybe my mind is playing tricks on me.

Brett

 

MIne is working like it should now. Used it on 160, 75 and 40 last night and today. 200 watts out with 100% mod. Just runs along..

Also fixed the valiant while I was at it.. 18K VFO resistor was TOAST along with a Melted oA2. This thing was melted bad. Put 6 watts of 18K outside the VFO and a new tube. Back up and running..

Thanks to all your help!

The:
Champion 300
Globe 500C
Valiant
Ranger

ALL WORK! (for now)

 thanks to the help I got from this board and people on the air. Thanks alot to everyone.

Clark