KLV-550

[bob85]

i don't know how you ended up with a volted supply if its the factory transformer, i guess rmitaly knew it was comming to the usa lol,

if you put a higher value resistor in place of the 1ohm to drop voltage it will make the bias regulation floppy under load,

you have much more fluctuation with temperature than i have seen before, are you sure the BD179 is bolted flat to the heatsink with a mica insulator and thin coat of thermal compound on both sides of the mica?

make sure you bolt the 179 and the board down before you solder the new 179, small details like that are important, there is NO room for error with biasing,

only one of the diodes wants to be sensing the top of the pills, the other diode should track the heatsink near to the bd179,

its tricky filing a flat then getting it down on the sink but with a new diode and carefull bending to put the flat facing straight down and carefull positioning with the board screwed down before you solder the diode from the topside it can be done,
if you put one of the diodes on top of the pill you don't deed to file it, just make sure its flat touching the pill cap,

use a blob of heatsink compound on the diodes,

yes you can remove r28 and feed the bias circuit from the regulated 13.8v supply by running a thin wire under the board, then adjust r30 to set your bias,

leave it alone untill your in the mood to mess with it and be carefull when you do,

good luck.

 

[liquidh8]

Yes, this is a USA amp,lol. i have a thin mica insulator and thermal grease for 179, I have plenty of replacement diodes for D15 and 16, so there are long leads on them and I can file them flat them to position them, one under the board, then have it pass through to the top, and the other on top of the pill, then right to ground on the screw between the pill.

The bias really does fluctuate alot, it shows on the power too.

I may just do the regulated power supply since it is only a small wire. I have an adjustable in r28 already, and i can feed 178 with that voltage. I'll try these things later on tonight.


Thank you for all the info, replies and help! I'll post my results when I do it tonight.

 

[hammer0630]

I am waiting on a Station 550 I just bought on eBay. The former owner states that he drives it with about 25 watts in order to get 300 350 watts out of it. This has me a little worried about the condition of this amp but he says it works fine. When i recieve it any day now I will find out whats going on. I am no tech but he states that it has a limiter for over-driving it but of course if you put to much wattage into it it you will have damage. I will see what goes on when I put 3-4 watts into it I can push 20-25 watts into it also if need be but that will definitely have me very nervous about burning it out.

 

[liquidh8]

if it has the 1407's in it it is too much.

Bob, for the life of me I can't figure out why it has 34 volts running to the 179. I redid the stuff with the diodes, one on the heatsink, another on the pill. and new arctic silver, yadda yadda. Put a new bridge rectifier in it. With the board unhooked, I get 28vdc out of the rectifier.

Needless to say I smoked yet another bd179, too much voltage I think. 34vdc, I left r28 unhooked and checked the voltage, but as soon as i hooked it up, smoke! before i did that, i hooked it up through the regulated voltage, but that is on all the time, so there is always a bias voltage being read at L9, even unkeyed. I am at a loss. I checked everything again, resistors, diode, transistors, everything seems good, but the voltage goes from 28 to 34 after hooking up the board.ugghhh:headbang:headbang

 

[bob85]

theres always voltage to r28 when the amps turned on but not on L9, you have something wrong in the bias circuit or the bias switching, check r29 tr8 and d17 again, it should not smoke 179's even if its turned on all the time,

is the amp still working with the bias disconnected?

 

[liquidh8]

Sorry, I think I mistyped it. When I have a line coming from the front 13.5 volt port, it is always hot, therefor, the bias is always on doing it that way. When the power switch is on and the standby is off that is.

As far as 179, I was looking at the specs, it says 110v in and 24v out for the xformer. Well, here in Pennsylvania, I have 126Vac in, so I am getting 34vdc everywhere. I wish i had a UPC so I can hook it up to a steady 110VAC. Since R28 was 0ver 700k ohm, it was allowing less voltage to 179, so it never fried, as soon as I put the one ohm back in, it fried them. I may have to put a DPST switch in for the standby (or a relay), and hook the bias up thru the regulated 13.5 vdc port, and do it like that. As long as the pills will stand 34volts instead of 30.

 

[bob85]

it makes no difference that the bias circuiit has power whenever the amp is on, don't worry about it, bias circuit is only turned on when you transmit ( when its working right ),

if you have bias voltage on L9 when you remove r28 and connect the 13.8v supply to the tr9 side of where you removed r28 the bias circuit is faulty or shorted,
if tr8 or r29 are oc the bias will be on all the time,

i never had 34v on the 179 so i don't know if it will stand it but i do know they are ok 30v or 13.8v regulated

 

[liquidh8]

I will check tr8 again, I have a transistor tester. to check it again.

I figured since the standby switch is off, (while power switch is on) there is no voltage to tr8's base, so it won't conduct, but there is voltage to tr9s base through me injecting the voltage, the 13.5 vdc that is always on regardless of the standby switch position, so it is conducting, and I am reading a voltage at L9.

Now with the standby switch on, I don't read a voltage at L9 unless I am transmitting like normal.

Is this right?

Maybe I could built a voltage divider for the input to drop 4 volts, but then again I have to worry about the current loss.

 

[bob85]

i get what you mean now, it would be, i wondered why you were talking about relays lol,
i never had any issues with mine but you can wire the 13.8v supply so it takes its power from the standby switch,

i disconnected the regulated supply from the front terminals

 

[liquidh8]

Ahh, that would be easier, lol, haven't thought of that.

 

[liquidh8]

Wel, I have the bias circuit powered by the 13.5 regulated supply. I used all new arctic silver for the transistors. I tried 3 different ways for the diode. The first is having D15 under the board, with a flat filed on it, and on the heatsink, and D16 on the left pill with a flat filed on it. The with just the diode on the heatsink, and lastly stock both on the top of the board.

I set the bas voltage with the amp cold.

with the first set-up, I could set bias voltage to be .62-.63, and after talking for 5 minute or so, it would drop to below .42 volts.

The second way, it would still drop, but to about .56.

The stock way, it would drop to maybe .59-.60 in high.

When did you check your bias voltage, amp hot, cold, throughout? Does it drop .2 volts while talking and the amp getting hot. If the bias voltage drops, the bias current is going up right, so that cant be good.

I am about ready to put the lid on it if I can get this right. I don't know what an original klv550 does.

FWIW, if the bias is over .65, it works and sounds good on the TX, but the power is down on setting 1-4.
The 1407's also don't like no more than 5-6 watts SSB before it gets overdriven sounding on power levels 5-6. KLV says 20watts, no way, lol. the spec sheet on the SD1407's say like 2 watts input on each pill, 125 watts min out. I can get 325 good sounding watts out of it.

 

[bob85]

i measure idle current as it heats up, i don't remember how much the bias voltage drops when its hot, its been a few years since i last went inside,

as the output transistors heat up they need less bias voltage for the same idle current, tracked bias will drop bias voltage to try and keep the transistors at the same operating point,

10wfm into mine shows about 300w out with the sd1407's, i don't push it any harder, im gonna try 422's and put the 1407's in an old ver200 i have.

 

[liquidh8]

i find the best way to do it using minimal test gear is,

adjust the bias for about 200ma increase in current draw from the dc side of the psu when the bias is manually activated in standby,

or remove L8 and insert an ammeter, set idle current to 200ma in standby with the bias manually activated,

I guess i could leave the ammeter in ln series and talk on the amp to get the thing heated up, to be sure I am still getting 200mA on it, no matter what the voltage. Since I am this far into it, I wanna get it as good as possible. Voltage is gonna be relevent only when I get the idle bias current right, I see that now.

I can't really have L8 out while talking to see if the bias is tracking right. I know some of those amps go into class C as you talk because the bias goes out of whack.

 

[liquidh8]

How many amps do you think the bias supply circuit uses? I have a plan, I built a little regulated power supply that'll take 40vdc (or a/c) in, and be adjustable for 0-40 out, I can turn it down to 24vdc to feed the bias so all is like stock, but it is only 1 amp. Would it draw more than one amp you think?

 

[liquidh8]

Or, how about I toss a 24v or 27vdc 5 watt zener diode after the 1 ohm resistor, this will give me a lower voltage. The preamp circuit uses a zener diode to bring it down to 12 vdc +/-. The 330ohm 2 watt resistor is in the wrong place on the schematic, but it is there. I could add a 24-28 volt zener diode right after R28 to knock a few volts off before the bias resistor and keep the voltage feeding TR9 in check.