Discussion in 'Amateur Radio Amplifiers' started by KC8QVO, Dec 26, 2019.
heard him call cq 3 or 4 times..he didn't work a soul... funny.
Actually, it's not even a typo.
The "single phase full-wave" shows "per tube" and indicates a FW CT circuit. Per tube .25A = .50A total for the circuit.
The "full wave bridge" shows "for four tubes" and .50A load current.
They are exactly equivalent. But a very screwy way to rate anything.
I recommended the 4-125 instead of a 4-65 mostly because the original post discussed "150W output," which the 125 can easily do, but a 4-65 would be straining to hit that.
Also, the 4-125 is very common and inexpensive.
The "glow" would come primarily from the filament, which is bright.
The heaters in indirectly-heated cathode tubes that run the heaters at lower temperatures: Not so much. Also, most of those require a minute or two "warm up," whereas the 4-125 is "instant on" and can be used within a second or two after powering it on.
Yes, it is.
The 866Jr is rated 0.125 amps per tube load current. Two in a FWCT circuit gives 0.25 amps total.
In a full wave bridge, two rectifiers are in series. You get more voltage but the same current.
The 0.5 amp load current in the last column is a typo.
That is what I said, typo
I know. I was replying to @WB2WIK
While it is possible to parallel four 807s/1625s in grounded-cathode, it's not easy to do so and have the amp be stable. And the higher you go in frequency, the harder it gets. Neutralization will be a must, as will getting tubes that are reasonably close in characteristics.
The OP presents us with a bit of a challenge in that there's only a few watts of drive power available. This rules out most grounded-grid designs because they typically don't have enough gain to provide 150-200 watts output with 5 or 10 watts of drive. In fact one reason grounded-grid amplifiers became so popular in the late 1950s/early 1960s was that they didn't waste the 50 to 100 watts of available driver power in an attenuator.
IMHO, the best solution would be the following design:
- Single 811A in grounded cathode (grid driven) A 572B could also be used.
- HV of 1250 volts.
- Zero bias Class AB2 operation
- Tuned grid circuit, link coupled, with neutralization
- Start out with a single-band design, probably 80 or 40 meters, but leave plenty of room on the chassis for bandswitches and tapped coil arrangement.
- External power supply. Depending on parts availability, either the classic pair-of-866As-full-wave-center-tap-choke-input-filter or the conventional silicon-diode-capacitor-filter-voltage-doubler setup for HV.
The result should be an amp that will produce about 150 watts output for about 8-10 watts of drive, and can do so on all modes.
73 de Jim, N2EY
150-250 watts, glow, big inexpensive tube? Seems to be ideal for single ended 813 amp. I just picked this home-brew amp from the estate
of Norm, N1PF. When I get a chance I'll be adding a second 813 and upgrading the PS to an AnTek transformer.
I agree that single tube is a bit easier. I'd recommend considering the 813 for a single tube for the additional power capability, lower drive requirement, and ease in adjusting power output via the screen. If not already on hand, $ will need spending on a transformer either way.
But, neither meets the four tube spec and both require more of a power supply.
This, at least, was my thinking in suggesting single band with four 807/1625.
Size is specified as NOT an issue so if, say a 40 m provides a lot of fun, then another band could follow.
Separate RF decks, leave room for plug in coils, or look for some switches. I'd keep it simple with separate decks.
Perhaps a push-pull of paralleled pair if higher bands are of interest?
Put the supply on it's own and use the same supply for each RF deck or other projects.
807/1625 requires a tad ~1/2 W drive/each.
I'm working on a single band 4-65 TX and also on a single band TX with a pair of 1625. Neither is finished. But, they are coming along.
The 4-65, while very attractive performance wise, requires HV.
I've assembled a 500 W microwave oven transformer based HV supply that works well.
Attendant HV tune cap is a PITA to find. Also, it's hard to find good 4-65s.
The 1625 TX power supply uses an old TV transformer I had on hand. It can easily power four 807/1625 tubes.
These transformers still turn up cheap at hamfests.
If I had 807s and sockets, it would not need the additional transformer to boost heater voltage.
The globe chief uses a pair of 807. http://www.ae5d.com/pdf/chief.pdf