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Re: SB-1000

 

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I believe the problem isn't the voltage itself, which would be found (measured) between gate and ground. The problem is knowing where, in the circuit, the input power is dissipated. The gate-to-ground connection is actually a kind of feedback loop, much like an input-to-gate connection with a resistor between cathode and ground, not decoupled by a capacitor.

?

I assume that part of the input power goes, among other things, to the output circuit. Why would this power be dissipated by heating the gate?

?

This doesn't mean that the gate doesn't heat up.

--

F1AMM

Fran?ois
Re: SB-1000

 

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Just to add some elements to the discussion. Here's what I noticed on my Drake L-7, so with 2 x 3-500Z. The -9V bias on the grid is generated directly on the grid; the 9V zener is not in the cathode circuit.

?

?

Note that the grid current is lower when the plate voltage increases.

?

In France, we're limited to 500W, but I wonder how in the USA you can reach 1 kW without exceeding the maximum Eimac values.

--

F1AMM

Fran?ois
Re: SB-1000

 

Pg=Vgc X Ig
Re: SB-1000

 

VK4TUX.? ?Nope.? that -75 vdc is for BIAS? voltage and only when operating Class C.... (either grid or cathode driven).?

Look under? cathode driven....and 0 vdc? bias voltage. U will see 215 V peak grid voltage.?
When u drive the cathode negative,,,,,,,? u are putting positive on the grid.?

I found that formulae buried in 1-2 places? re grid diss.? No clue where I discovered it.?
It is indeed...... Peak cathode voltage X? DC grid current = grid diss.?

That 1 kw pep out in the? SB-1000.....and also the AL-80B? ?is the ...'ICAS'? rating....... or as Bill Orr calls it.... the IVS? (intermittent voice service)? rating....... both terms are used for SSB only.?
Per W8JI,? who designed those amps ( the heathkit version was licensed from Ameritron)? the 1 kw pep out rating on the single? 3-500Z? was fully approved by EIMAC.?

Once tuned up..........? while talking on SSB,? you will notice that the AVERAGE DC plate current....and also the AVERAGE? ?DC grid current is only 1/2 of the key down CXR value.? ?This is how they can get away with the 1 kw pep out on SSB? ( and also 850 w out on CW)? ?rating on that amp.? ?IE: lower duty cycle.? ?

Here is another eimac spec sheet.? ?I would not run the tube at their stated? zero bias....... idle current is way too high.? It needs bias.? ? 50 ma? for idle current is ample.?
https://frank.pocnet.net/sheets/088/3/3-500Z.pdf
Re: SB-1000

 

Yes, that’s what Eimac says typical grid should be. I Eimac also states max limits:
Ig 108mA
Ip 400mA
max output 740W
?
but Heatgkit SB-1000 and AL 80B must have special permission from god. Their manuals say max limits are:
Ig 200mA
Ip 550mA
output 1000 watts
?
To do this, you will need to drive the exciter around 100W and you will exceed the typical 75V grid and likely porn up your 3-500Z.?

In other words, ignore the manual limits and just follow the Eimac data sheet limits and you won’t exceeded your grid dissipation?
Re: SB-1000

 

开云体育

> The Eimac formula for grid dissipation is:

> Pg=Vgc X Ig

?

I can't find this magic formula in the Eimac documents I have. Could you post this document or a URL that allows us to find it?

--

F1AMM

Fran?ois

De la part de Adrian Fewster via groups.io
贰苍惫辞测é?: mercredi 16 avril 2025 03:18
Re: SB-1000

 
Edited

1st,
voltage squared divided by resistance equals power.?
?
2nd,
The Eimac formula for grid dissipation is:
Pg=Vgc X Ig
where Vgc is the peak positive grid to cathode voltage
and Ig is the DC grid current.
?
example:
100W X 115 = 11,500 and extracting the square root = 107.2V RMS.?
107.2 X 2sq (1.4) = 150V?
?
150 X 0.2 =30 and so 30W of grid dissipation is exceeding Eimac 20W of grid dissipation by 50%.?
Re: SB-1000

 

开云体育

Eimac states driving impedance is 115 Ω

grid dissipation = peak voltage X grid current.?
so at 100W drive, peak grid voltage is 150V

150V X 0.2Ig = 30W grid dissipation. ?30W

?

I don't think you can calculate the power dissipated on the grid this way : grid dissipation = peak voltage X grid current.

What are your sources on this interesting topic?

I don't know where the 100W of the input are dissipated.

?

If your formula is good, it would be very worrying.

--

F1AMM

Fran?ois

De la part de Adrian Fewster via groups.io
贰苍惫辞测é?: dimanche 13 avril 2025 22:56
SB-1000

 

I own a Heathkit SB-1000. Have not had it to long, just a few months. Had a few issues and just wanted to share them and what I did to fix them.?

one day on 80M I think I hit a bad something. Bad tune or wrong ant, I’m not sure but had an arc or something. After that, 80 was not tuning up at all. 40M and up worked fine but ones in a while, I could swear I seen and even Hurd an arc. I thought it was the tube, but it was just the reflection off the tube that is visible through the right side cabinet. This started happening more and especially while tuning up. And the breaker kicked off the amp and it went back on.?

I took the cabinet off and had a good view at the area that I suspected was arcing and I noticed the wire from the wound core L9 to the band select was broken. There was a small gap between the wire and the chassis about 1/8 or less and I seen it arc across.?

Also, turn 11 on the 80M/160m tank L8 was tarnished black and the plastic form/turn spacers were melted to the point that the shape collapsed into two pieces, pushing into each other with some of the turns, touching each other. ?

Also, the 2.5mH RF choke fried. It lost value but was not open. This agile junctions with the lead to L9 wound core wire that broke.?

I replaced the RF choke, fixed the wire, pulled the L8 tank out, cleaned with toothpaste, water mix, rinsed with water, then rinsed with 91% alcohol, Fabricated plexiglass, spacers and reformed the tank.?
I also used strips of paper soaked with DeoxIT to clean the relay contacts, a trick I learned from my friend Paul. I tested all of the diodes on the rectifier board, inspected everything, tightened all bolts, including the loose ones that hold the tube socket, they also ground the grids. I did the washer mod on the band select junction that runs to the door knob, capacitor on the plate capacitor to prevent corona. I cut many long leads at many junctions from the original builder. and I cleaned everything.?

now she is working great, here is some of the data I recorded after tune up on several bands.?

160M
68W drive = 600W out
Ig = 150mA
Ip = 380mA
Vp = 2900
Zp = 7632
input = 1,102W
efficiency = 54.45%
?
?
80M?
62W drive = 800W out
Ig = 150mA
Ip = 425mA
Vp = 2900
Zp = 6824
Input = 1,232.5W?
efficiency = 65%

40m
63W drive = 810W out
Ig = 150mA
Ip = 400mA
Vp = 2910
Zp = 7275
input = 1,164W
efficiency = 69.6%
?
20M and 15M Efficiency about 63%

10M?
58W drive = 700W out
Ig = 150mA
Ip = 435mA
Vp = 2900
Zp = 6667
input = 1,261.5W
efficiency = 55.5%

I have ran about 10 hours or so since I repaired the amp and I’m pretty happy. I do not run the limits in the manual, the manual max limits are:
Ig = 200mA
Ip = 550mA
Output power = 1KW
thats nuts and contradicts Eimac data sheet for a 3-500Z
?
Eimac Data sheet max at typical operation at 3KV
Ig = 108mA
Ip = 400mA
output 740W
?
Heathkit manual max limits = 37.5% over Eimac max specs and has you exceeding grid dissipation by 50%. Grid is the most fragile part of the tube.?
Eimac states driving impedance is 115.?
grid dissipation = peak voltage X grid current.?
so at 100W drive, peak grid voltage is 150V
150V X 0.2Ig = 30W grid dissipation. ?30W grid dissipation is 50% over Eimac 20W Grid Dissipation.?

I do runs a little over on SSB, about 150mA of Ig and 400mA of Ip, but on CW I run a max of 100mA of Ig and/or 400mA of Ip, no more.?

well, thanks to my friend Paul for his great mind and others!!!
?
thanks for reading. Hope this helps someone out there.?
KG2RG
Re: Commander HF-2500 meter lamps and HV PS

 

Jim, VE7RF,?
that is a boatload of FB info!!! I had not had a chance to respond but have read it twice and may need to read it a few more times and drill it in. Thank you!!! Great contribution to me and likely many others too.?
AL-80A tx led removal

 

Is there a way to remove the red tx led without taking off the front panel?? I cannot see in the back because of the large filter caps.? TU ..Bill?
Re: CTR Engineering/W8JI Response?

 

Tom is great. Just email him again
Re: Commander HF-2500 meter lamps and HV PS

 

开云体育

Yeah. Weird.

It printed out fine here.

"Email me at gudguyham@.... Lou"

Alek VK6APK

On 13/04/2025 12:31 am, Steve wrote:

Come to think of it... if your ISP won't display A O L dot com, then it may not even allow you to e-mail to A O L dot com.


On 4/12/2025 9:26 AM, Steve wrote:

"That" was supposed to be "at A O L dot com" without the spaces. Your ISP probly doesn't like the A O L part and removed it.

Steve K0XP


On 4/12/2025 8:27 AM, KG2RG via groups.io wrote:
gudguyham@.... Lou.
what is that??? ? Not an email?
--
See my QRZ.com page at
--
See my QRZ.com page at

Re: Commander HF-2500 meter lamps and HV PS

 

Ok, thanks. I just emailed you Lou
Re: Commander HF-2500 meter lamps and HV PS

 

Whoops @aol.com. Sorry




On Saturday, April 12, 2025, 11:27 AM, KG2RG via groups.io <justinandyazny@...> wrote:

gudguyham@.... Lou.
what is that??? ? Not an email?
Re: Commander HF-2500 meter lamps and HV PS

 

开云体育

Come to think of it... if your ISP won't display A O L dot com, then it may not even allow you to e-mail to A O L dot com.


On 4/12/2025 9:26 AM, Steve wrote:

"That" was supposed to be "at A O L dot com" without the spaces. Your ISP probly doesn't like the A O L part and removed it.

Steve K0XP


On 4/12/2025 8:27 AM, KG2RG via groups.io wrote:
gudguyham@.... Lou.
what is that??? ? Not an email?
--
See my QRZ.com page at
--
See my QRZ.com page at

Re: Commander HF-2500 meter lamps and HV PS

 

开云体育

"That" was supposed to be "at A O L dot com" without the spaces. Your ISP probly doesn't like the A O L part and removed it.

Steve K0XP


On 4/12/2025 8:27 AM, KG2RG via groups.io wrote:
gudguyham@.... Lou.
what is that??? ? Not an email?
--
See my QRZ.com page at

Re: Commander HF-2500 meter lamps and HV PS

 

gudguyham@.... Lou.
what is that??? ? Not an email?
Re: Commander HF-2500 meter lamps and HV PS

 

Email me at gudguyham@.... Lou




On Friday, April 11, 2025, 8:05 PM, KG2RG via groups.io <justinandyazny@...> wrote:

Lou, can you email me. I’m interested in one of those boards for a future fun project. My Email is good on QRZ.
I’ll also try and see if I can private message you here. Not sure how that works but I’ll start clicking on everything hi hi. ?
Re: Commander HF-2500 meter lamps and HV PS

 

Plate load Z? =? loaded B+ / (1.8 x? DC plate current).?

On all those old amps, the higher voltage was always 41.4 % higher than the lower B+ setting.? ?The DC plate current was 41.4%? higher, when in the higher B+ setting.?

You can use different V ratio's as well.? ?IE:? ?1/2 the loaded B+? and 1/2 the loaded? DC plate current, and now you have 1/4 the power.

You can use any B+ ratio you want.? ?( as long as the current ratio uses the same ratio...which implies careful control over the drive levels).

In all cases the plate load Z? remains the same.? It works superb.?

?And works much better? if using lower power data modes.... vs? using the existing high B+ rating......and reducing plate current in 1/2.? ?That fubar method results in doubling the plate load Z.......? which then screws up the tank values.? Double the plate load Z, and you now require? 1/2 the value for the Tune and load caps..... and double the uh on each band.? ?Since you didn't do that, the tank Q just doubled =? lousy tank eff....and circulating RF current in the tank coil and bandswitch remains the same.? And with data modes, the average dc plate current is double that of processed? SSB,? so now the amount of watts? dumped into the poor tank coil and bandswitch has quadrupled..... and you just cooked the bandswitch.? ?It's just I squared x? R.? ? In this case it's? RF current? squared x? ESR? ?ESR is effective series resistance...aka? RF resistance.?

IE:? Ameritron? 'big 3'? amps being driven to 1/2 plate current...... while stuck using the oem? B+.?
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