Royce 1-642 final bias adjustment

[3pinplug]

Hi all
I want to check the bias after fitting new finals, the Pace 8193 sams info that i have for it(same board i believe) says the following:-
Insert a 0-500ma DC meter at “TP11” ( junction of L5 and C77).
Ch19, usb,xmt, power mic minimum.
Adjust VR14
Final bias adjust for 80ma
Well TP11 i couldnt see marked on the sams info i have? So put meter on positive side of cap c77 which would be the junction with L5 but no reading?
Anyone ever checked tjis and is that the correct way for the royce or aimed just at the pace?
Hope someone can help, can post up the relevant part of schematoc if that helps?
Thanks
Mark

[Sandbagger]

May 6, 2021 8:26:59 GMT -5 3pinplug said:

Hi all
I want to check the bias after fitting new finals, the Pace 8193 sams info that i have for it(same board i believe) says the following:-
Insert a 0-500ma DC meter at “TP11” ( junction of L5 and C77).
Ch19, usb,xmt, power mic minimum.
Adjust VR14
Final bias adjust for 80ma
Well TP11 i couldnt see marked on the sams info i have? So put meter on positive side of cap c77 which would be the junction with L5 but no reading?
Anyone ever checked tjis and is that the correct way for the royce or aimed just at the pace?
Hope someone can help, can post up the relevant part of schematoc if that helps?
Thanks
Mark

A current meter is not read by probing a test point and ground like you would for a voltage reading. A current meter must be put in series with the load you are trying to measure. Most radios with bias adjustments have removable jumpers that you pull out and then put the current meter in place of the jumper. Most Typical solid state CB radios bias current runs anywhere from 25ma to 50ma on the final. 80ma seems a little high, but if that's what the service manual calls for then ok. Be careful of the information found in SAM's manuals. Misprints are very common.

[2600]

Like the man said, you have to break the circuit feeding power to the final transistor. The current meter is clipped one lead to each side of the break. That way, the current you're measuring passes through the meter. Just don't leave the radio set to AM mode. The normal current drain will trip the fuse found in some current meters. Has to be set in SSB mode. Upper or Lower doesn't matter.

Don't have a mental picture of that radio to go on. Some older radios would extend two bare wires out of the circuit board and then lap-solder them together. Separating them provides the two attachment points for your meter leads. They get soldered back together when you're done.

Been too long since looking inside one of those.

73

[3pinplug]

Hi
Thank you both for this it has been really helpful and appreciate you taking the time to reply.
It says insert at Junction of L5 and C77 so i will have a look and see if any wires like you mention are present and report back.
Regards
Mark

[3pinplug]

Hi all

Had a look in the raea and have taken some pics which may help, at the junction of L5 and C77 there is one other item a wire as shown - have included the ciruit daiagram of the area as well.

Do you think that jumper wire (best way to describe it) should be disconnected?

Hope this helps.

[2600]

The link wire gets clipped. One end of each probe wire on the current meter goes to one side of the cut. Lap solder them back together when you're done.

73

[3pinplug]

Thats great i will cut it and see what reading i get , thanks again, will report back on what i find.

[3pinplug]

Hi all

I managed to set the final bias and got myself up and running again, however I was getting random reports on SSB from closer stations that my mod was sounding funny. After enough of these I thought I better check it so looked for the pot to adjust the SSB mod but couldn't see one.

I have the Royce 1-642 but am working from the Pace 8193 Sams as that is supposed to be the same chassis. Looking by the XMTR driver i have found a VR control - labelled as "VR13" but this is not shown or listed anywhere in the Sams for the Pace 8193. It stands vertically on the board where as all the others are horizontal.

Its located on top left at the rear of the radio just in front of the Xmtr driver.

Any Royce  owners know what this VR actually does, I really didin't want to go just moving it so thought best to check on here first.

Thanks all

Regards

Mark

[2600]

I'm at home, and Sams CB280 is at work. Hopefully. Just can't refer to it right now.

What first comes to mind is to ask how the sideband ALC was set.

There's more than one way to sound "funny". Improper bias setting is only one of many.

If the ALC was set for max wattmeter reading instead of max audio clarity that could explain it. A second radio you can use to hear a radio that's transmitting is incredibly useful. Relying only on what others tell you about your signal is error prone.

73

[3pinplug]

Hi
I set the SSB RF ALC as per the pace 8193 sams instruction, it says to set it to max 12 watts which I did. Not familiar with the radio so just following the sams as this is all I have.
So are you saying when setting the SSB RF ALC don't set it for 12 watts, I should adjust it for best Audio.
This evening i have just discovered the final MV1-Y was not working, not sure if this could be a factor?
Thanks
Mark

[3pinplug]

Just looking at radio and also noticed that 2 black wires are connected to the upper tab of the "2SC1061" (Q17 AM Regulator I believe from the schematic only deviuce of this type on schematic )  - as shown in the photo below. Is this wiring factory? and it should be there?. The tab where the wires are connected has 13v on it at all times , don't normally see a connection like this so wondered if anyone can confirm if that is right.

Thanks again everyone.

Mark

[Sandbagger]

Jul 9, 2021 13:55:51 GMT -5 3pinplug said:

Just looking at radio and also noticed that 2 black wires are connected to the upper tab of the "2SC1061" (Q17 AM Regulator I believe from the schematic only deviuce of this type on schematic )  - as shown in the photo below. Is this wiring factory? and it should be there?. The tab where the wires are connected has 13v on it at all times , don't normally see a connection like this so wondered if anyone can confirm if that is right.

Thanks again everyone.

Mark

View Attachment

That looks like the thermistor that is usually attached to the driver and final. Its job is to respond to increases in temperature and reduce the bias proportionately to prevent thermal runaway. Why it's on the AM regulator, I have no idea.

[2600]

Yup. It's a temperature sensor/compensator. That type transistor tends to draw more current as it warms up. The bias circuit needs to track the temperature and turn the bias down in step with temp rise.

Setting ALC without a 'scope can also be done with an average-reading wattmeter. Find the end of the ALC trimmer that shows max modulated power on the average meter. Now turn the trimmer slowly the other way while modulating with your voice until you see the wattmeter reading suddenly "dive" to a reading around half or less the "wide open" reading.

The threshold at which the sideband limiter kicks in and begins to work tends to be pretty sharp. This method works almost as well as watching the waveform on a 'scope for "flattopping" of the modulation waveform. My favorite method.

Of course, you can do this with a true (active) peak-reading meter. But you won't be watching for a drastic drop in power, but a small drop of a few Watts.

73

[3pinplug]

Hi Both
Thankyou for your help it is very much appreciated.

ALC
I have a scope so sounds like your preferred way is to do it so i will give that way a go, do i modulate the signal with a two tone or single tone (say 1000hz). The key point i am looking to set it at is just before the point of the flat topping using the scope method or do i also monitor the watts drop off at same team, my power meter is only an swr/ rf watts output type is that ok?

This is great information and increasing my knowledge so thanks again for helping.

[3pinplug]

Forgot the second part about what looks to be just two pieces of wire. These are on the pcb in the middle far right of pcb, the xmtr driver and final are top left of pcb so some distance apart so not sure by their physical location they could be fitted to the final. They look just like two wires similar to the wire you cut when setting the bias.

[3pinplug]

Hi again, one further thought in addition to the two bits above. On the final bias is there a tell tale sign you have it right? Like for the ALC you see a power drop any signs for the bias setting being right or just use whats specified?

[Sandbagger]

Jul 10, 2021 0:11:53 GMT -5 3pinplug said:

Hi Both
Thankyou for your help it is very much appreciated.

ALC
I have a scope so sounds like your preferred way is to do it so i will give that way a go, do i modulate the signal with a two tone or single tone (say 1000hz). The key point i am looking to set it at is just before the point of the flat topping using the scope method or do i also monitor the watts drop off at same team, my power meter is only an swr/ rf watts output type is that ok?

This is great information and increasing my knowledge so thanks again for helping.

Two things to keep in mind. 1, the 12 watt setting is for FCC compliance, not necessarily the point of cleanest waveform. 2, The ALC is normally set for max clean power. When you use the scope, use a 2 tone audio signal and after adjusting all of the coils for max power (with ALC wide open), you back the ALC down to the point where the peaks of the waveform on the scope are nice and rounded, with no flat topping. If the transmitter is capable of 18-20 watts flat out, you may be able to see 14 or 15 watts with a clean waveform. No need to back it down further. Too much ALC can make the audio sound "choppy", depending on how the ALC circuit is designed.

[3pinplug]

You certainly know your stuff thanks for this i will try this in the morning, over in the UK so very little info on these radios over here.
Do you have any tips / tricks for setting the final bias in case i have done that wrong as well.

Thanks again for taking the time to help.

[Sandbagger]

Jul 10, 2021 14:00:35 GMT -5 3pinplug said:

You certainly know your stuff thanks for this i will try this in the morning, over in the UK so very little info on these radios over here.
Do you have any tips / tricks for setting the final bias in case i have done that wrong as well.

Thanks again for taking the time to help.

Setting the final bias isn't as scary as it seems. If you can't get the proper current number, there is an alternative method to setting it. Using the 2 tone audio signal, you can set the bias while you are transmitting SSB into the scope. Start with no bias and slowly adjust it until the waveform shows a clean rounded pattern instead of a sharp cutoff at the negative trough where it meets the centerline. This method may not be as exacting, but you will be able to set it for clean modulation.

[3pinplug]

Hi Sandbagger

My modulation appears to have what I can only describe as an echo when monitored on another radio but I have no echo fitted. I have also just discivered a VR control to set the driver bias, so I need to :-

1. Set the driver bias now but there does not appear to be a wire to cut like there is for setting the final, do I have to lift a leg on the component to do this?

2. The ALC VR trimmer doesn't appear to make any difference to the modulation so I am assuming someone has been in and maybe disabled the ALC, not sure I will have to identify that part and check.

3. Have also discovered that someone has lifted a leg of Capacitor C1 and fitted a tuning can in line with it,a ssuming this is some sort of receive mod I have no idea but mabe this is also affecting the modulation I have no idea what it is for, all I know is its not supposed to be there.

Have posted some pics of the above.

Thanks

Mark

Attachments:

[Sandbagger]

Jul 14, 2021 13:03:36 GMT -5 3pinplug said:

Hi Sandbagger

My modulation appears to have what I can only describe as an echo when monitored on another radio but I have no echo fitted. I have also just discivered a VR control to set the driver bias, so I need to :-

1. Set the driver bias now but there does not appear to be a wire to cut like there is for setting the final, do I have to lift a leg on the component to do this?

2. The ALC VR trimmer doesn't appear to make any difference to the modulation so I am assuming someone has been in and maybe disabled the ALC, not sure I will have to identify that part and check.

3. Have also discovered that someone has lifted a leg of Capacitor C1 and fitted a tuning can in line with it,a ssuming this is some sort of receive mod I have no idea but mabe this is also affecting the modulation I have no idea what it is for, all I know is its not supposed to be there.

Have posted some pics of the above.

Thanks

Mark

That someone disabled the ALC/AMC is highly probable. So many people like to do that. The driver bias is less critical. You can probably set the pot to mid range and you'll be close. Otherwise you'll have to break the connection leading to the driver's collector (preferably on the supply side of the blocking choke)and insert the milliamp meter there. Make sure you are on SSB and absolutely no modulation, otherwise the current reading will be excessive and inaccurate.

As for the extra can, that's a head scratcher. The first thing I thought was extending clarifier range. But where it is placed is nowhere near the clarifier circuit. It sucks working on a radio that someone frankesteined. It makes it tougher to get back to stock condition again.

[3pinplug]

Thanks i will have a look and report back on progress.
Appreciate this.
Regards
Mark

[3pinplug]

Hi
I have managed to get a copy of the actual 1-642 schematic and now find 2 x VR’s that need adjusting when you cut the wire link, looking round do i connect to the emitter leg of the driver and set bias, then connect to the final emitter leg and set bias, would legs be left in situ or lifted? As there are 2x vr’s where as previously i had ammeter across the broken link anyone know how i connect it all up now? Would a post of the area showing the 2x VR’s on the schematic help?

[2600]

The meter leads probe to either side of the clipped wire. Although a gator clip on the end of each meter wire would be easier. The gap from cutting the wire is now bridged by the meter. And that's how you measure current, by passing it through the meter.

73

[3pinplug]

Hi
Thanks for reply much appreciated. If i clip across wire and had only one VR to adjust then i follow that but appears I have : to adjust. I will post a scan of the bias / final area as it may be this orher VR is not part of the bias circuit, i do not know what the extra VR is for but from the diagram hopefully someone will recognise it.
Thanks

[3pinplug]

Hi all

Trying to add attachement of a scan scan of the actual schematic for the Royce 1-642 not the sams 8193 one, it shows the 2 x VR's that I have - VR13 & VR14.

but keeps saying i have exceeded the 1 meg limit but its only 143KB - anyone know where i am going wrong, it worked on a previous post on here?

Once i cut the link wire, from looking round the net would I then lift the leg on the Bias and Final and then adjust individually the idel current for each whilst measuring the value on the relevant lifted emitter leg of each component?

Also seems that 50ma is the min required across most radios so what should I set at, 50, 60 or the 80ma as shown in the Sams?

[2600]

I predict you won't hear a difference between 50 mA and 80. It's not a critical adjustment, since it will drift up and down with temperature rise and fall.

Odds are that if it's in that ballpark, you're good to go.

73

[3pinplug]

Hi 2600
Thats good to know, many thanks.
Still unsure of procedure though as previously i cut link wire then put ammeter across cut wire, then if i only had one VR i would adjust this to show 60ma on meter across broken wire. However as i have potentially 2 VR’s to adjust assuming i do them indiviually. As no answer via board on the two VR’s i will lift the emitter leg on each and see if i can adjust that way with the meter across lifted emitter leg to ground.

[3pinplug]

So disconnected link wire, lifted emitter leg of driver and final, thenconnected dvm between emitter leg and ground in 200ma setting but no readings. Even repeating this when i reconnected the link wire - nothing!
I am at a loss now , what does VR14 and VR13 actually do as i cant see how you adjust both individually, maybe one is nothing to do with the bias setting - are there any 1-642 owners or previous owners eho know how to set the bias on this radio?

[Sandbagger]

Nov 20, 2021 14:49:13 GMT -5 3pinplug said:

So disconnected link wire, lifted emitter leg of driver and final, thenconnected dvm between emitter leg and ground in 200ma setting but no readings. Even repeating this when i reconnected the link wire - nothing!
I am at a loss now , what does VR14 and VR13 actually do as i cant see how you adjust both individually, maybe one is nothing to do with the bias setting - are there any 1-642 owners or previous owners eho know how to set the bias on this radio?

Why are you lifting the emitter leg? By doing that along with the wire link, you are creating an open circuit. Lift the wire link only and put the current meter in series with the wire link to measure bias current.