BC610

[K9ACT]

I have a friend with a BC610 having trouble getting it up and running.

The plate choke has a 700 ohm resistor in parallel with it and it gets so hot that the board under and around is scorched and charred.  The resistor and choke are still in tact but I am curious about the purpose of the resistor and also why the value of the choke is so high (25 mH).

js

[W2PFY]

That resistor is listed as R-9 and is a parasitic resistor. Maybe the transmitter needs to be neutralized? I have been working on BC-610's for about thirty years and never knew the resistor to get hot. The choke is 2.5 MH, not 25 MH. The resistance through the choke should be about 8,5 ohms.  If its way high from that value, it could explain why the resistor is getting hot. The resistor needs to be separated electrically from the choke for proper measurement.  Also look for a path to ground from that board. If  is charred to ground, It should be taken off and cleaned or replaced. If the path to ground is present, it may be extremely hard to correct it but it can be done in some cases, if you want to work like a dentist drilling & blasting away

If you have the right material, it should not be hard to replace it.

[Ralph W3GL]

Yeah, what Terry said!

[N8ETQ]

  Hi..

  Either way the choke is open. I have a bunch of the National
4 pie chokes here, the measure ot at 45 ohms. My 610 E
measures 54 ohm from PA plate cap to the plate side of the tank
coil.  If there was a carbon track in there I would think it would
be tripping the overload relay.

GL & 73
/Dan

[K9ACT]

  Hi..

  Either way the choke is open.

Could you elaborate a bit?

What are the either ways?

js

[N8ETQ]

Sorry OM,

 I was refering to W2PFY's post.. sorry.

/Dan

[W2PFY]

Sorry OM,

 I was refering to W2PFY's post.. sorry.

The book says it 8.5 ohms. I'm trying to help  K9ACT. Please explain why you think the choke is open? You may be right if that resistor is the only thing in the path to the PA anode.That would really make the resistor hot if not blow out. As far as the overload relay is concerned, there was no mention of that event. I was just trying to cover all the basses     Good points, check the resistance of both.

[K9ACT]

The resistor measures nominal and the choke "has continuity" in the words of my friend.  I don't think he can measure the L but we know it is not open.

I will ask him what the DC resistance is.

js 

[N8ETQ]

   I think if the resistor was shorted out by an 8.5 ohm choke
the resistor would not get hot.  ONTH if there was a carbon
track in there, 700 ohms would dumping the Over Load relay
pretty reliably.  Again, I measure out at 45 ohms from the plate
cap to the "Hot" side of the tank coil.  Someone mentioned
the LF Mod. Testing into a dummy load there should be no reason
you couldnt just jump out the 700 ohm R.  as part of that mod was
to jump out the whole parasitic choke thing anyway.

Please lety us know what you find.

73
/Dan

http://users.ameritech.net/dharlan/dans.htm

[W2PFY]

It would be interesting to know the plate current and how much grid current is flowing.

The grid current should be at least 60 mills and I have seen 100 mills on the lower bands.

The mod current should idle at 40 mills. Lower is ok but higher idling current really lites up the 100TH tubes.  This is when its run on the 2 KV tap.

[N8ETQ]

well, do you have the manual and the speech amp.

Ig around 100 on 75m
Ip around 200 ma

The modulator current meters are in the speech Amp
on anything that would have been called a 610. I think
the HT4 had one on the rig itself.. can't recall.

So what kind of 610 we talking about?

/Dan

[W2PFY]

ONTH

What does this mean?

[KX5JT]

ONTH

What does this mean?

on the other hand?? maybe that was what it was supposed to be

[ke7trp]

What band is the resistor getting hot?

C

[k7yoo]

Read the manual:
 
The component is supposed to be removed for 160M operation. I set mine with a small knife switch to take it in and out of the circuit

The early HT4 and BC610B models had audio level meters in the speech amps and mod current meters in the rigs. Later models had mod current meters in the speech amps.

Skip

[Gito]

Hi


The manual wrote that the RFC (CH4) with it's distributed capacitance forms a parallel -resonance  circuit at frequency between 2 and 4 mc ,
that means when we operated the transmitter at some frequency between 2 and 4 mc,that's works on this parallel -resonance circuit,
 there will a high RF voltage developed across this CH4 and because R 9 is in parallel with it ,it will dissipated  a lot of power,depended on the RF voltage .
Just a though


Gito

[N8ETQ]

Read the manual:
 
The component is supposed to be removed for 160M operation. I set mine with a small knife switch to take it in and out of the circuit

The early HT4 and BC610B models had audio level meters in the speech amps and mod current meters in the rigs. Later models had mod current meters in the speech amps.

Skip

    Nice solution Skip...  Mine was to just add a "Regular" Parisitic choke
in the plate lead and jump that crap out from the start.  The knife sw.
is Sweet,  Gotta say never even thought about that.  Funny how different
people approach the same problem.

     I had forgotten about the 610-A , B. C. They sure were Pretty rigs.
The 610-E changed every thing in SCR-299 except for that "Classic"
look.

73
/Dan

   

[K9ACT]

Here are some comments by Dan, W9GOB on where he is at:

Hello Jack. thank you for getting all the comments, the latest on the rig is this.

1.  I removed the whole big tunning capacitor and on the bottom of it are the resistor and choke. with it removed and placed upside down on very carfull examination and just plain dumb luck I saw that the resistor and choke are connected together on one side by a heavy silver plated solid wire that goes to the tank coil and carriys the H.V.,,,,,, well the solder contacts on both choke and resistor had hair line cracks 100% around the joints and the wire could actualy be moved around. I used a big iron and made the repair. put it all back togther and instantly had rated power and NO parisitic action !!! I started to think I had it fixed BUT once again after about three minutes on the air there was more smoke and the resistor was very very hot. so I shut it down..

2. This morning K9WEK and his xyl came over on their way to see their son in Batavia and Dan looked at the prints etc. He noticed that the main plate tunning cap was fully UNMESHED at reonance [dip] I saw that before too and thought it a little strange. he thought maybe the coil was misslabled or defective.. I did try it with some shorted turns of the coil and that did bring the capacitor plates to dip at a more 'meshed' position but not by very much.....
3. also we clipped out the resistor and were running on the choke only [ it is true the resistor is to be out of the circuit below 160 meters so its there as a parasitic suppressor device above  2 megs ,, so now the situation is.
 4 no more smoke ..5 capacitor still has only a small overlap of plates at resonance[dip] and I am back to only getting 100 watts out of it? 

6 I guess next thing to do is change the choke    thank you dan

..................

I vote for getting rid of the resistor permanently.  I suspect there is nothing wrong with the choke and it would seem that there is something wrong with the coil if it resonates with the cap nearly open.

js

[N0WEK]

Interesting!

I guess Dan W9GOB bought another BC-610. I bought his last two, an E and an I model a couple of years ago.

[Gito]

Hi


Maybe the designer knows of this Bc 610 is prone to self oscillation in .(low -frequency parasitic oscilation)

So to block this oscillation ,A RFC (CH4) with R9 in parallel is connected between midtap of C12 to the midtap of L7 .

To broaden the the HF response/lowering the Q of CH4 ,a R9 is placed in parallel with CH4,the purpose of R9 is to prevent parasitic oscillation in the choke and dissipates unwanted RF energy.

Looking at R parts of the manual it is written that R 9 =630 ohm +/- 5% with  18 watt rating.

Looking at it (18 watt) maybe ,it is design to absorb a lot of heat.

So maybe R9 (18 watt) must be design to dissipate a lot of heat ,comparing the heat 0f a 10 to 20 watt soldering Iron?

And maybe there' no problem with the transmitter?

And maybe I'm wrong

when R9 is omitted  ,the transmitter will not work properly?

And maybe I'm wrong !!!!


Gito

[N8ETQ]

Here are some comments by Dan, W9GOB on where he is at:



2. This morning K9WEK and his xyl came over on their way to see their son in Batavia and Dan looked at the prints etc. He noticed that the main plate tunning cap was fully UNMESHED at reonance [dip] I saw that before too and thought it a little strange. he thought maybe the coil was misslabled or defective.. I did try it with some shorted turns of the coil and that did bring the capacitor plates to dip at a more 'meshed' position but not by very much.....
3. also we clipped out the resistor and were running on the choke only [ it is true the resistor is to be out of the circuit below 160 meters so its there as a parasitic suppressor device above  2 megs ,, so now the situation is.
 4 no more smoke ..5 capacitor still has only a small overlap of plates at resonance[dip] and I am back to only getting 100 watts out of it? 

6 I guess next thing to do is change the choke    thank you dan

..................

I vote for getting rid of the resistor permanently.  I suspect there is nothing wrong with the choke and it would seem that there is something wrong with the coil if it resonates with the cap nearly open.

js

  I think with R9 being wire wound and not shorted out by CH4  you
have a lot more "coil" in there than you think you have.  Good to hear
it made full output for a while.  No worries, Its almost fixed!!

  Still wonder what model of 610 were talking about. The resistance
measurement from the Plate cap to the center pin on the coil
jackbar WILL tell the tale.

GL

/Dan

[Gito]

Hi


When the manual wrote parasitic oscillation.I believed it means low -frequency Parasitic Oscillation,in triode amplifier ,

with rf chokes used in both plate and plate circuit,the split stator  tank circuit combine  with  the r.f choke forms  a low -frequency parasitic circuit (from the ARRL handbook)
.
So the purpose of R 9 is to block/prevent this oscillation and to absorb the energy.

The manual said the Rf choke is a parallel resonance circuit at 2 to 4 mc .

actually between the C.T of the coil and the CT of the split stator has small RF voltage ,

I believed  the CT of the coil caries the smallest RF voltage and the biggest RF current.
 It's the RF voltage between this two CT, not The DC voltage .

 So if there's a RF voltage across the R 9 .it dissipated a "small" power in this R  and  CK 4 has a relative low impedance,unless  the the split stator or the CT tap of the coil is not have equal value anymore.

But approaching the frequency of the Parallel resonance of the CK4,CK4 becomes a high impedance,
As we know if we fed  a parallel resonance circuit with the RF voltage with the right frequency it will gives the highest peak voltage across this circuit,depended on the Q factor of the circuit.

So at this frequency a lot of power is dissipated in R9.

Gito