Go from 200uF to 350uF in HV P/S
All of my Caps in my Kenwood amplifier are 500V at 200uF, total of 8 thats 25uF when done. if I change them to 500 V at 350uF that will give me 43.75uF when done. do I benefit any from that? The amp was made in 1992 and I just want to change them out to be safe.
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Probably better to have posted this as "Amplifer Power Supply". Increasing the total C in your supply may be benificial or not ! It depends !!!!! For SSB use, I would have thought that 25uF was about adequate. Higher duty cycle modes may benifit from an increase C but increasing the C's will increase the "inrush" current through the rectifier diodes etc, perhaps leading to eventual failure. I would have thought that Kenwood would have taken all this into account. I would stick to the old C values, to be on the safe side, if I were you.
Perhaps W8JI and others could give you better advice.
Worth while going onto W8JI's web side. Covers most aspects of amplifier design and operation.
Dave is correct.
I heard about a young ham who built a 4-1000 amplifier years ago. He got to a point where he could put it on the air, except that he didn't yet have the filter capacitors. He went ahead anyway. As unbelievable as it may seem, as long as he used SSB and didn't run the speech processor, you could not tell it.
Just goes to show how little (in his case, zero) HV filter capacitance is required.
START by downloading and using the Kenwood TL-922 Service Manual
All of my HV Electrolytic capacitors in my Kenwood amplifier are 500V at 200 uF, so when the total 8 are used produces 25 uF when done.
IF I change them to 350 uF units (at 500 V), that will produce a total of 43.75 uF.
VK2FC Photos of his HV capacitor replacement of TL-922(A)
Some of the vaccum tube audiophiles go to larger values to stiffin their HV supplies.
This same question about HV capacitor repalcement for the TL-922(A) was asked on eHam.net in 2009.
Gordon, N6WK has a detailed answer of the replacements he ordered from Digi-Key.
A few points that you have to watch for:
1. FIT into SPACE (SIZE). The larger uF capacitors may be taller; have wider lead spacing; or have a larger diameter.
In some cases, the new components will not fit the existing space.
Fortunately, CDE and other mfg. supply all of these specifications on the Internet, so you can check before ordering.
Advances in material sciences over the past 3 decades have decreased the overall size of electrolytic capacitors for a given value.
2. BLEEDER RESISTORS. As a part of normal maintenance, you will want to check (measure values with DVM/VOM and visually inspect)
the bleeder resistors in the HV stack. In some cases, you may want to change the resistor's value for the additional capacitance.
3. 500 VDC Electrolytics. A few years ago, 500 VDC electrolytic capacitors were difficult to get -- due to product decisions and changes by mfg.
Fortunately, the Inveter and SMPS markets have increased demand for these values and the selection has improvded over the last 5 years.
CDE (also own Mallory brand name) in the United States is still the largest producer.
4. LOAD LIFE. As you select your replacements, pay attention to the LOAD LIFE specification.
You will have several to choose from (1,000 to 8,000 hours at 85 to 125 C) -- some are much better than others.
CDE Electrolytic Capacitors (catalog page) - SCREW Terminal and SNAP-IN types
IF this is the Kenwood TL-922(A) HF amplifier, then the original units are likely ELNA or Panasonic components --
I have found the Panasonic components to be excellent units and good for at least 20 to 25 years in nornmal usage.
Last edited by W9GB; 12-01-2010 at 06:13 PM.
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Increasing the amount of capacitance will only increase the low frequency audio response of the amplifier, and your exciter should not be outputting much if any signal below 300hz or so.
You are allmost doubling the capacitnace, I wouls just about expect failure in the rectifier diodes in the future.
If it was my amp, I would stay with the values Kenwood used...
Now my mistakes travel at the speed of light!
Ive used 330 and 470uF cps as replacements for 160-270uF as used in most older amps as long as a step start was included when built or added with the caps.
The added filtering wont be noticed but it may improve the PEP on amps with less than robust transformers but this may also raise the transformer temperature in a contest type enviroment. There is no free lunch. The TL-922 transformer is more than adequate.
Increasing the Power Supply filter capacitance will increase the audio low frequency response of the amp?
Originally Posted by AI3V
At most, it should slightly improve the voltage "regulation" of the power supply under load; resulting in slightly less voltage drop under load.
I am using eight 450v 470µF capacitors for 59µF in a dual 572B amplifier. A little overkill, but i'll be using soft start so it 'should' be OK
Power supply is around 2250V so each cap will have about 280V across it so they should be happy!
I'd also replace them with the same values as original. If its not broke, don't break it
I'm sure Reg realize the output of a rig is at 1.8-30 MHz and NOT at or even close to 300Hz.
Originally Posted by M0UKD
The problem is the TUBE in the PA converts the RF back to audio frequency loading on the power supply by changes in the power of the envelope!!!! Loading on the power supply, because of this, is at an audio rate. Because loading variation follows the change in the envelope, and because that change is at an audio rate (both syllabic and pitch), any severe slope in voltage over the duration of a rising or falling load can add distortion. The saving grace is with reasonable capacitance any IM products would be at a very low frequency, so bandwidth would not be affected nor could anyone really hear it.
Because of that, and probably because Kenwood went well over the "knee" of the curve where more capacitance helps stability and to reduce ripple, I don't think you will see any change.
It worked out in the AL12 series amps 15 uF was out on the flat part of the curve, and this was with a 10 ohm ESR transformer and 3000 ohms of load during peaks. I doubt the Kenwood has nearly that ESR with the tiny E-I lamination core compared to a tape wound grain oriented transformer with interleaved windings, although being a doubler would push up the requirements.
I would assume you are safe using what KW spec'd, and I doubt inrush is capacitance dominated (except for time) so I doubt peak currents would change much even if you tripled capacitance.
The most common worry for what you propose would be damage to components in an arc, because more energy is stored. Even that is very slight for the change you propose.
My guess based on a bunch of highly likely assumptions is nothing much would change. Use whatever is cheapest and easiest, but don't get crazy and use something unreasonably large.
Last edited by W8JI; 12-06-2010 at 08:00 PM.