Yes I concur with this suggestion Steve. With only 200 Volts on the screen in AB1 linear mode the 4CX1500B tubes are likely being starved and held back like variously reported amongst 8410 amp users.
Good point that you make here Glenn. My comment about optimum screen voltage for unconstrained Po was predicated on the assumption the design value of cathode NFB resistor(s) was still correct and ha
Jim, This ominous scenario here sounds to me a precursor to the company going down the proverbial gurgler....you can't ignore the client interface and customer service; it is absolutely critical to m
Most odd situation here Ken...in any business operation you can't ignore the client interface and customer service like that; it is absolutely critical to maintaining enduring good will and strong re
My commiserations over having all three tubes fail like this Bob. Other than failed or ineffective protection circuits that might have caused grossly excessive input over-drive to the grids, or an ab
Yes, these grid and screen dissipation ratings / limits are indeed the reason why efficacious protection mechanisms in the amplifier design that respect and conservatively accommodate these dissipati
Precisely Carl. Agree with your comments about Eimac tubes being designed and built to CCS specifications and their associated excellent longevity. I am of the conservative school of belief that one
You're right Jim about the former invention and clever marketing promotion of the so-called "4CX800" tetrode tube by a bunch of entrepreneurs! Nevertheless some commercial amplifier vendors notably A
All good points you make here Jim on which I concur with. I agree SDR rigs are not yet prime time and certainly not well suited to out of the box appliance operator hams. They are more for technicall
Hi Alek, Although I've not tried it, a less dramatic technique here might work: If the tungsten / molybdenum wire welded into a basket forming the 572B's grid structure is sufficiently ferromagnetic
Hi Ron, I tried a magnet on some old 811A broken internal electrode parts including the grid basket and they stick to the magnet....so there might well be scope for correcting the electrode misalignm
Yeah running a tetrode based muscle amp as a linear for AM is problematic and caution must be exercised in obtaining optimal plate loading and choice of plate load line not causing excessive power to
All good comments here Jay. But you omitted to speak to the subject line and offer an opinion on the likely reason why the pair of FU728 tubes both failed with grid to cathode shorts? What did the ow
I agree here Jeff. Sans doing a hi-pot test on the tube as Jim suggested verifying its withstanding voltage, I'd install a fast HV fuse and glitch resistor in series with the plate feed, enabling the
Hi Mike, In view of this experience, I'd suggest running the tubes with a lower plate voltage circa 3 kV max if that can be easily facilitated. I suspect the premature tube failures experienced now e
Bottles like the 4-1000A thrive on such high plate voltages, but the internal close-spaced electrode construction of the GS35B (designed for UHF service) with its oxide coated indirectly heated catho
I concur with your comparative assessment of the three tube types here Lou. The 8877 is the indisputable ?gold standard? for QRO ham amplifier triodes?.its a pity it is now so damn expensive :-( To e
A most excellent concise summary here Gary.... Leigh VK5KLT Mark, First let's define classes of operation: Class A, plate current flows over 100% of the cycle of the input signal. Class B, plate curr
I concur with all that Alek has said here about sourcing quality Russian military surplus RF parts....especially NOS tubes. Leigh VK5KLT Dr Alex. UR4LL. I wouldn't deal with anybody else. Best prices
That's correct Alek.....the 3-1000Z must be treated the same as a 3-500Z, i.e. the anode must be gotten cherry red in order to activate the residual gas absorbing Zirconium getter coating on the anod