29 Jun
2011
29 Jun
'11
6:57 p.m.
Testing my 2m-8877 after several months QRT, I am only getting 800w
output. That is partly due to only achieving 30w drive from the
FT-847 (but it drives into a dummy load at 50w). Peaking the 8877
input does not increase either drive or output. Output is also
peaked (should not require much tuning as it was not changed since it
last ran at 1400w and SWR is nearly the same). Anode current is low
as a result. HV is normal and grid current is a little low (typ. of low drive).
I checked filament voltage and it is only running 4.6 vac (whereas it
used to run 4.9-4.85 vac). Could the low filament voltage be
affecting the input impedance and explain the low RF output? Is
this indicative of a failing tube?
I have one higher tap on my filament transformer that will apply
higher voltage to the filaments. I can try that to see if it raises
the filament level. With filament and cathode disconnected the
filament transformer is running (open circuit) at 5.06 vac. The
transformer is rated to 11 amps at 5vac.
When I last ran the amp in February, I was running 1300-1400w but
after about 20-30 minutes of one-minute transmit cycles power dropped
to zero and anode voltage was 2500v vs 3700v. I didn't troubleshoot
further but was suspecting a drop in HV as the cause. I do not know
what was causing that but was planning to try duplicating the
condition, today. But with the amp running as it is I may have other
issues. Probably not good to run the filaments that low very long.
73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-?
DUBUS Magazine USA Rep dubususa(a)gmail.com
======================================
29 Jun
29 Jun
7:54 p.m.
New subject: [Moon-net] 8877 filament current draw
OK found two changes that have me up to 1300w:
!) Replaced an undersized machine screw in the barrier strip that
clamps the filament lines. Fil =4.8v
2) Switched coax jumpers from the FT-847 to the Bird Meter and drive
jumped to 50w.
The second change either points to the fact that SWR is high on input
making line length critical to getting a good match?
I checked filament resistance (cold) with ohmmeter comparing with my
spare 8877 and both show initially about 0.3 ohms. 5v/11a = 0.45
ohms. I suppose filament resistance changes as they heat up.
I think I will swap taps on the fil. transformer to get loaded
voltage closer to 5v. That ought to increase output.
At 02:57 PM 6/29/2011, Edward R. Cole wrote:
Testing my 2m-8877 after several months QRT, I am only
getting 800w
output. That is partly due to only achieving 30w drive from the
FT-847 (but it drives into a dummy load at 50w). Peaking the 8877
input does not increase either drive or output. Output is also
peaked (should not require much tuning as it was not changed since it
last ran at 1400w and SWR is nearly the same). Anode current is low
as a result. HV is normal and grid current is a little low (typ. of
low drive).
I checked filament voltage and it is only running 4.6 vac (whereas it
used to run 4.9-4.85 vac). Could the low filament voltage be
affecting the input impedance and explain the low RF output? Is
this indicative of a failing tube?
I have one higher tap on my filament transformer that will apply
higher voltage to the filaments. I can try that to see if it raises
the filament level. With filament and cathode disconnected the
filament transformer is running (open circuit) at 5.06 vac. The
transformer is rated to 11 amps at 5vac.
When I last ran the amp in February, I was running 1300-1400w but
after about 20-30 minutes of one-minute transmit cycles power dropped
to zero and anode voltage was 2500v vs 3700v. I didn't troubleshoot
further but was suspecting a drop in HV as the cause. I do not know
what was causing that but was planning to try duplicating the
condition, today. But with the amp running as it is I may have other
issues. Probably not good to run the filaments that low very long.
73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-?
DUBUS Magazine USA Rep dubususa(a)gmail.com
======================================
_______________________________________________
Moon-Net posting and subscription instructions are at
http://www.nlsa.com/nets/moon-net-help.html
73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-?
DUBUS Magazine USA Rep dubususa(a)gmail.com
======================================
9:23 p.m.
New subject: [Moon-net] 8877 filament current draw
Hi Ed,
Class AB2
Fil is 5.0 (+ or -) .25 volts current is min 9.5 to 11.5 amp.
cathode warm up 180 sec
Here are the EIMAC tube spec for 30 Mhz
Plate Voltage 2700 3500 Vdc
Cathode voltage + 8.2 + 8.2 v -- I use a 12v zanier for
this voltage
Zero sig Plate Current 92 ma. 182 ma.
Plate Current 740 ma 1000 ma
single tone grid current 40 ma 74 ma
Two tone grid 16 ma. 25 ma.
Peak drive power 40 w 64 w -- this drive is to cathode
Singe tone POWER 1085 2075
Here are the EIMAC tube spec for -- 220 -- MHz or in your case 144 MHz.
AB2
Plate voltage 2500 Vdc
Cathode voltage +8.2
Plate Current 1000 ma -- Idle is 92 MA.
Grid Current 10 ma. -- off the 220 MHz spec sheet -- see
30 Mhz (40 ma.) for what I use
Output Power 1520 W
Drive power 57 W
Power Gain 14 db
If you want the class B op conditions can send those, but looks as your
running in AB2 condition.
VERY IMPORTANT ---- I would suggest that you measure on the 8877 tube fil
pins directly,
and be sure that it is at least 5.0 to 5.25v for a old tube,
that is to keep the cathode emission up and not starve the cathode of
current reserve / operating temperature
Hope you have a final fix for the amp, as the 8877 is a power house if run
correctly, will last you years of op time,
my various 8877 amps when I run them loaf at +1500w out @3200 v.
tom W2DRZ
http://www.w2drz.ramcoinc.com/
http://www.w2drz.ramcoinc.com/ProgNotes.htm
----- Original Message -----
From: "Edward R. Cole" <kl7uw(a)acsalaska.net>
To: <moon-net(a)mailman.pe1itr.com>
Sent: Wednesday, June 29, 2011 7:54 PM
Subject: Re: [Moon-net] 8877 filament current draw
OK found two changes that have me up to 1300w:
!) Replaced an undersized machine screw in the barrier strip that
clamps the filament lines. Fil =4.8v
2) Switched coax jumpers from the FT-847 to the Bird Meter and drive
jumped to 50w.
The second change either points to the fact that SWR is high on input
making line length critical to getting a good match?
I checked filament resistance (cold) with ohmmeter comparing with my
spare 8877 and both show initially about 0.3 ohms. 5v/11a = 0.45
ohms. I suppose filament resistance changes as they heat up.
I think I will swap taps on the fil. transformer to get loaded
voltage closer to 5v. That ought to increase output.
At 02:57 PM 6/29/2011, Edward R. Cole wrote:
Testing my 2m-8877 after several months QRT, I am
only getting 800w
output. That is partly due to only achieving 30w drive from the
FT-847 (but it drives into a dummy load at 50w). Peaking the 8877
input does not increase either drive or output. Output is also
peaked (should not require much tuning as it was not changed since it
last ran at 1400w and SWR is nearly the same). Anode current is low
as a result. HV is normal and grid current is a little low (typ. of
low drive).
I checked filament voltage and it is only running 4.6 vac (whereas it
used to run 4.9-4.85 vac). Could the low filament voltage be
affecting the input impedance and explain the low RF output? Is
this indicative of a failing tube?
I have one higher tap on my filament transformer that will apply
higher voltage to the filaments. I can try that to see if it raises
the filament level. With filament and cathode disconnected the
filament transformer is running (open circuit) at 5.06 vac. The
transformer is rated to 11 amps at 5vac.
When I last ran the amp in February, I was running 1300-1400w but
after about 20-30 minutes of one-minute transmit cycles power dropped
to zero and anode voltage was 2500v vs 3700v. I didn't troubleshoot
further but was suspecting a drop in HV as the cause. I do not know
what was causing that but was planning to try duplicating the
condition, today. But with the amp running as it is I may have other
issues. Probably not good to run the filaments that low very long.
73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-?
DUBUS Magazine USA Rep dubususa(a)gmail.com
======================================
_______________________________________________
Moon-Net posting and subscription instructions are at
http://www.nlsa.com/nets/moon-net-help.html
73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-?
DUBUS Magazine USA Rep dubususa(a)gmail.com
======================================
_______________________________________________
Moon-Net posting and subscription instructions are at
http://www.nlsa.com/nets/moon-net-help.html
4356
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Edward R. Cole -
w2drz