Solid Stated Warrior... HV on all the time?

[KC4KFC]

More advice please.  This is my first experience with an amp.  I have read that once the Warrior has had its rectifiers replaced with diodes, to keep the HV on at all times.  Somehow, I would think it would be easier on the finals, the four 811A's, to give some warmup time before applying HV.

One more.

If I key the amplifier with no input, do I still need a load?  Just wondered if I can warm it up and read the HV and idle plate current without the dummy load.

Thanks for the info.

Mark

[w4bfs]

hi Mark ... I am wondering if while you replaced MV rectifiers with 'bricks' if you also added a HV step-start circuit ... if not, you will probably get a 'thump' when you hit the HV switch ... this may or may not be destructive depending your effective uncharged supply impedance (composed of several things: transformer impedance in both primary and secondary sides, diode on resistance, any chokes, and capacitor esr) the step start adds an additional impedance to the primary side and then as the inrush current subsides, shorts out the additional resistance... highly recommended to add ... testing amp HV without a load depends on whether or not it is keyed ... most amps are setup to insert amp operating bias  when keyed ...not necessarily so with older ones ... bottom line is if operating bias is presented to amp tubes, then a dummy load should be connected in case it should oscillate to (hopefully) prevent damage ... hope this helps ...73 ...John

[John K5PRO]

I wonder where you heard that you need to keep the HV on all the time with SS rectifiers? Tain't so.... I suppose that there was a switch for filaments when it had 866's that either had a timer or you waited before throwing the HV. With SS, you don't need to do this, you can just switch the HV on anytime, after defeating the warmup circuit for the 866s. Besides, the 811As would be happy to have HV applied after they are warm. The Heathkit SB220 amp does apply HV as soon as the filaments start heating, with one switch. Thats because it has 3-500Z triodes which have very fast warmup filaments. And, of course, it has SS rectumfinders.

As for testing no load, possibly risky if it is not unconditionally stable amplifier. If you don't have a dummy load yet for full power, however, you can just use a small resistor, 50 ohms, as long as you are not giving your Warrior any RF drive.

[WQ9E]

I think John is right in that the major concern with the SS replacements would be the turn on surge since the series impedance is going to be a bit less than that of the MV rectifiers.  If you don't want to add the "relay/resistor" type step start then I would suggest at least adding inrush current limiters to the primary of the HV transformer.  These only cost a few dollars, are soldered in series with the primary leads with no other modifications, and offer a fairly significant resistance when cold which will greatly reduce the initial current surge.  The only real weakness with inrush limiters over the relay/resistor route is that they do have a bit of thermal time constant once up to operating temperature and if the power is removed for only a few seconds (generally less than 15) they will not increase to their normal "cold" resistance in time for the next power on cycle.  However in practical use this isn't generally too much of a concern because if the power is just removed for a few seconds your filter caps probably won't be fully discharged either.

Rodger WQ9E

[WBear2GCR]

It's been a long time since I had a Warrior here.

It's a zero bias set up, iirc - no bias on the 811s, or self bias?? - but a look at the schematic would tell that quickly. You can download one from the BAMA site that is shown in the banner above this thread - above - look for it! 

I seem to remember that there is a front panel switch to turn on the HV... but I might be remembering another unit. Again, a look at the schematic will tell you if there is a switch between the HV supply and the tubes or not - and if it also controls the filaments or not (that means it is usually just the power switch). It's often labeled "standby/operate".

One could put in a simple circuit (assuming the solid state HV PS) that uses a capacitor to charge up over a few seconds to pull in a relay. The purpose of the relay is to be open circuit when the unit is turned on, and then after the filaments in the 811s are hot, the relay turns on and applied the B+.

Or you could just go back to tube type rectifiers, or alternately use a single tube rectifier in series with the solid stated full wave rectifier - the only purpose there is to provide the delay needed to keep the HV off the plates of the 811s until the tube is conducting. One might be able to use a "TV Damper Diode" tube for this, they are low V drop and handle a great deal of current and voltage. Since the DC is already present, and it might be placed after the filter it will only see a small voltage drop across it anyhow and very little ripple... might be a good way to go.

The other thing is that there may be a bit of a momentary but heavy load if the AC line is simply switched on with a solid state rectifier present - the cap is trying to charge up fully instantly. That can be prevented with a "step start" - that is a relay that when you turn on the rig is OPEN, but a resistor of suitable size is across it, and in series with one leg of the AC line, then the relay closes after a few seconds (sound familiar?) and it is becomes a direct connection. The key is that at the start, the PS has its current limited by the series resistance, then after it closes there is no current limiting. Typically that resistor will be 25-100watt size and perhaps something like 8 to 20 ohms in value depending on the actual current draw of the amp. In most cases the momentary current load on turn on for an amp as small as a Warrior can be ignored, but you might notice a flicker in the shack lights on turn on - that's an indication of the instantaneous current draw.

             _-_-bear

[W2XR]

As I indicated in an earlier post on this topic, I also have a Heath Warrior HA-10 amplifier that I use in conjuction with my Heathkit Marauder HX-10 transmitter.

I had converted my Warrior to the plug-in "solid-state sticks", as replacements to the original 866A mercury vapor rectifiers. Converting to SS rectification also removes the load from the 2.5 VAC transformer that provides filament power for the 866As, pretty much eliminating this transformer as a potential point of failure.

There is no need for a soft-start current limiting circuit in the plate supply of this amplifier. All you have to do is let the 811As warm up for a few seconds, as they are directly-heated thoriated tungsten filament tubes, and then flip the HV plate switch on. You are charging an 8 uf filter capacitor thru a 5 to 50 hy swinging choke (choke input topology, of course), and the choke has a significant DCR component that limits the instantaneous charging current, thereby reducing the inrush stress on the rectifier stacks.

Many Warrior owners have successfully converted their amplifiers to solid-state rectification without any soft-start; in fact, I personally am not aware of any that did add soft-start.

The Warrior does have a bias circuit to cut-off the 811As when you are in the Receive mode; this is done to eliminate the possibility of the amplifier generating spurious noise that could be heard in the station receiver. It is good practice to replace the 1000 uf @ 15 VDC filter cap in the bias supply as a matter of routine overhaul, as this capacitor does become leaky over time. It is the only electrolytic in the amplifier; the 8 uf capacitor in the HV supply is a high quality oil-filled cap. When testing the amplifier, you must jumper the bias interconnect terminal strip on the rear of the amplifier, or the 811As will draw excessive plate current. Normally, the bias interconnect is connected to a pair of dry contacts within your transmitter.

If you don't have the manual for your Warrior, I suggest that you obtain one before firing it up, so you can familiarize yourself with the testing, tune-up, installation, and operating procedures.

Good luck with your Warrior; plug in the solid-state rectifiers, use it, and enjoy it with no worries. It is a classic piece of equipment from the golden age of ham radio!

73,

Bruce

[ka3zlr]

I've Stepped started alot of things even the 30 amp Astron DC P/S's I have, it's a Feature that's relieves a possibility and compliments a circuit.

[K1JJ]

Mark,

Normally, you can key the amp and draw idling plate current with no problems. You should be able to key and twist all the tuning knobs and the plate current should remain stable. If not, then there is a stability problem. A GG amp should be very stable.  Just don't key AND put in RF drive without a 50 ohm output load on the amp or damage can occur.


Another method to turn on the HV to keep the surge current on the SS recifiers low...

1) Cheap and dirty:  Add a filter choke in the center tap of the power transformer to ground, or add one to the CT of the bridge SS stack to ground. A choke will limit the surge when first turned on AND give better regulation to the supply when the amp is keyed.

2) Cheap and dirtier:  When using 120V, no choke and don't desire to add a step-start relay, then replace the "on-off" plate power switch with a DPDT (double pole, double throw) CENTER-OFF switch.  Then wire the toggle-down to turn the supply on with the 10 ohm 25 watt resistor in series with the ac primary to charge the caps slowly. Then 3 seconds later flip the switch UP wired so the 2nd pole connects the ac without the series resistor for normal operation.  Return the toggle to center and you are All-OFF.

Though, when working with 240V and two poles, using a step-start relay is a good way to go.  Actually here, I use two, two pole breakers to manually step start my 240V HV supplies, not relays.


Yes, as the guys said, HV can stay on all the time with SS diodes. What was probably meant is NOT to TR key the HV on and off w/o some form of current limiting. Charging caps directly with diodes can result in tremendous current surges limited only by the xfmr's winding resistance.

BTW, the final shake-down AM acid test that many of us egg each other on to do: Sock a continous "Yallo" into the mike while rapidly keying the TR on and off. This separates the borderline from the robust rigs. Most ricebox/linears can do it easily, but plate modulated rigs with the inductive iron spikes can blow things. Spark gaps on the iron and big rig step-starts recommended...

Good luck!

Tom, K1JJ

[KC4KFC]

Thanks for all the help, guys. I will look into the step start concept to try to understand it better, but I feel ok now in just letting the the 811's warm a bit before turning on the HV.

I do have the manual and schematics and recommended mods.  Also operating instructions and parameters.

Idle bias voltage is recommended -4.5 v and I measured -4.35 v. The receive mode bias cutoff voltage needs to be anything from -40 to -90 I think. I guess the matching exciters of the day from Heathkit would provide this but I will  have to rig up something external. I wonder if this needs to be pure dc or if I can just bridge rectify a small transformer and use that.

I ordered some solid state relays from Fair Radio that I will use both for the bias cutoff voltage and the interface to an Icom or any modern rig. I'll put it in a box with a standby switch.

The Warrior has a monitor rca jack that I was going to try to tie into my oscilloscope, TEK 2500 series (I think).

Charging caps directly with diodes can result in tremendous current surges limited only by the xfmr's winding resistance.

That's the thing. I would hate to lose a xfrmr....


This forum is and has been a great resource and I really appreciate it!

Thanks and 73

Mark KC4KFC

[WBear2GCR]

It is very likely that the Warrior generates its own internal bias voltage.

Again, check the schematic to see if there is some line labeled "-XXvdc" or similar, where XX is some number like the 45 volts mentioned.

The external part/jack is probably only the control for the circuit, not sending bias voltage to the amplifier...

I would have downloaded the schematic and had a look, but it is 2.4meg on BAMA, and I'm on a turtle slow dialup out here in the Soviet of New Baltimore NY... 

                  _-_-bear