smoking-amp / jazbo8,
Often, error in datasheets can occur. I have an 70's RCA tube handbook from Argentina (in Spanish, not Portuguese or English), and have an error with 6AQ5A: in the plot says 150V to g2, where it should be clearly written 250V ... suddently the 6AQ5A becomes an high perveance tube in these manual!
To be sure I checked this using my µTracer with NOS 6AQ5A tubes, and see another datasheets.
Of course, high gain/high gm tubes naturally have loosely specs, unless if factory selected ( = Special Quality, SQ).
Often, error in datasheets can occur. I have an 70's RCA tube handbook from Argentina (in Spanish, not Portuguese or English), and have an error with 6AQ5A: in the plot says 150V to g2, where it should be clearly written 250V ... suddently the 6AQ5A becomes an high perveance tube in these manual!
To be sure I checked this using my µTracer with NOS 6AQ5A tubes, and see another datasheets.Of course, high gain/high gm tubes naturally have loosely specs, unless if factory selected ( = Special Quality, SQ).
Both the RCA-GB and the Westinghouse-Japan tubes have only painted on markings, although quite different printing and ink color. No etchings. The Westinghouse has the usual yellow paint for its logo, and gold like paint for the 6HB6 with a trimmed box around it. The RCA has orange paint for the logo and white paint for the 6HB6. Everything else about them are Xerox identical: micas, plates, getters, even the cathode sleeves have the same distinct angled cut-off at the top end. The Westinghouse has a 4J code under the made in Japan marking. The RCA logo has an odd ET. code under it. Neither are using the later dark emitter heater wires that RCA came out with. Curves are reasonably matched.
The other RCA tubes (beamers) here do have an etched on: 6HB6 U.S.A. and an odd dot pattern. The dot pattern is different on different tubes.
The other RCA tubes (beamers) here do have an etched on: 6HB6 U.S.A. and an odd dot pattern. The dot pattern is different on different tubes.
Last edited:
I pulled out my box of 6HB6 tubes here to look through them. Got them all years ago on sale. Mostly GE, then RCA, half dozen Raytheon, 5 Sylvania, and a few Motorola, Westinghouse, and singles of Dumont, Lindal and ITT.
I looked through them to see what construction they had:
("windows" denotes small window slots in edges of plates)
Lindal: 1 real pentode - Japan (exact same again)
Zenith: 1 beamer/windows, USA
Westinghouse: 1 real pentode - Japan, and 1 beamer/no windows, USA
Motorola: 2 beamers/windows, USA
Dumont: 1 beamer/windows, USA
ITT: 1 real pentode - Japan (exact same)
Raytheon: 1 real pentode - USA (gold 6HB6 lettering, just like the
Westinghouse! identical to the JAPAN ones!),
3 beamers/windows, USA, CFA/CFA/CFF8 etch
Sylvania: 5 beamers/windows, USA, 1 beamer/no window, USA, CFA etch
RCA: 4 real pentode - GB, look just like the JAPAN ones
43 beamers/windows USA, 2 beamers/no window, USA, CFA etch
GE: 66 beamers/windows USA, 16 beamers/no window, USA, CFA etch,
4 beamers/no window, USA, no CFA etch
So to sum it up:
8 real pentode, probably all JAPAN (absolutely identical)
120 beamers/windows USA
24 beamers/no windows USA, mostly CFA etch
Most of the RCA and GE beamers with windows look like identical construction.
The CFA etched no window beamers look the same. A lot of these were marked 6HA6 only, but some are marked 6HB6 too. All have the same size plates as the windows 6HB6/6HA6 versions.
I think I will put the windows, versus non windows, beam versions on the tracer next to see if there is any difference.
I looked through them to see what construction they had:
("windows" denotes small window slots in edges of plates)
Lindal: 1 real pentode - Japan (exact same again)
Zenith: 1 beamer/windows, USA
Westinghouse: 1 real pentode - Japan, and 1 beamer/no windows, USA
Motorola: 2 beamers/windows, USA
Dumont: 1 beamer/windows, USA
ITT: 1 real pentode - Japan (exact same)
Raytheon: 1 real pentode - USA (gold 6HB6 lettering, just like the
Westinghouse! identical to the JAPAN ones!),
3 beamers/windows, USA, CFA/CFA/CFF8 etch
Sylvania: 5 beamers/windows, USA, 1 beamer/no window, USA, CFA etch
RCA: 4 real pentode - GB, look just like the JAPAN ones
43 beamers/windows USA, 2 beamers/no window, USA, CFA etch
GE: 66 beamers/windows USA, 16 beamers/no window, USA, CFA etch,
4 beamers/no window, USA, no CFA etch
So to sum it up:
8 real pentode, probably all JAPAN (absolutely identical)
120 beamers/windows USA
24 beamers/no windows USA, mostly CFA etch
Most of the RCA and GE beamers with windows look like identical construction.
The CFA etched no window beamers look the same. A lot of these were marked 6HA6 only, but some are marked 6HB6 too. All have the same size plates as the windows 6HB6/6HA6 versions.
I think I will put the windows, versus non windows, beam versions on the tracer next to see if there is any difference.
Last edited:
Hmmm, good!
Some little tips to perfecting this project:
For monitoring cathode current, you can put an 10R resistor between the cathode and ground, so you can calculate the anode dissipation to limit value to 10W (adjusting g1 bias) and get long life to tubes.
Some people can put 560R-1k in series with screen grid to protect them against current peaks, and helps agains some instabilities.
You are using regulated screen supply, is good for pentode amps.
Maybe to use 5k loadline, you can bias the screen grid with more voltage (the datasheet limit is 300V) and gain some power, but don't forget to adjusting the g1 bias to compensate total bias, in that case.
Is good to use different tubes/valves and learn from this. Some time ago, I built a 14W PP amp with 6EM5 tubes, with great results. The 6EM5 is another EL84-sized beam "tetrode" with low odd harmonics so provides low THD in PP amps.
Good luck with your new project!
Some little tips to perfecting this project:
For monitoring cathode current, you can put an 10R resistor between the cathode and ground, so you can calculate the anode dissipation to limit value to 10W (adjusting g1 bias) and get long life to tubes.
Some people can put 560R-1k in series with screen grid to protect them against current peaks, and helps agains some instabilities.
You are using regulated screen supply, is good for pentode amps
.Maybe to use 5k loadline, you can bias the screen grid with more voltage (the datasheet limit is 300V) and gain some power, but don't forget to adjusting the g1 bias to compensate total bias, in that case.
Is good to use different tubes/valves and learn from this. Some time ago, I built a 14W PP amp with 6EM5 tubes, with great results. The 6EM5 is another EL84-sized beam "tetrode" with low odd harmonics so provides low THD in PP amps.
Good luck with your new project!
Isn't 390V too high for the plate? The maximum rating is 300V, also the bias is way too hot.
This link appears to be a flaw in our forum because I just I added an "smilie" at the end of the sentence, and this "missed link" appeared in the place of smilie, at the time I published the message.
Sorry about that...
Yes, with various tube/valve types that have the anode size of EL84 (including EL86, 6EM5, 6HB6, 6973, etc ...) have the ability to provide around 20Wrms in PP mode, but each falls into a somewhat different class of load and voltages / currents operation. When I built my amplifier with 6EM5 I was lucky to find an 6EM5 equivalent tube, the 7558. In the data sheet of 7558 indicates operating conditions to SE, PP and RF amplifiers, making easy my job. Does 6HB6 have some equivalent with complete data sheet?
Another way to estimate the maximum output power is to analyze a known complete datasheet (with audio conditions) tube that has the knee voltage with Vg = 0V coincident and same/close maximum dissipation, as I successfully did once with 12AL11 (but I no longer remember which valve had such "equivalence", but it might be easier to just make the load line
).
Nah, in fact, I suspect the data given in the datasheet isn't quite right, besides, it does not show the typical operating conditions for push-pull operation. The best thing is to have some actual measurement results once the OP builds the amp, so we make the proper adjustments to the datasheet figures as needed. If I have some time next week, I will try to put it on my prototype board and run some quick tests with the Raytheon 6HA6 that I have, but don't hold your breath.Does 6HB6 have some equivalent with complete data sheet?
Another way to estimate the maximum output power is to analyze a known complete datasheet (with audio conditions) tube that has the knee voltage with Vg = 0V coincident and same/close maximum dissipation, as I successfully did once with 12AL11 (but I no longer remember which valve had such "equivalence", but it might be easier to just make the load line
I have an amplifier design called a Tubelab SPP. It was designed for use with EL84/6BQ5 or EL86/6CW5. If I run NOS 6BQ5's or JJ EL84's I can run 430 volts of B+ with a regulated screen supply of 310 to 325 volts depending on the tubes. With a 6600 ohm OPT this combination makes 25 to 30 watts RMS at 5% distortion without red plate or tube death using 6BQ5's. 6CW5's want a much lower screen voltage and a 3300 ohm load.
I had such an amp running for about 2 years with Sylvania 6BQ5's that were plucked from a discarded Baldwin organ. It was used as a computer sound system so it was on a lot. Most modern "EL84's" and "7189's" will red plate and fry in this set up.
I cut the traces and rewired the sockets for 6HB6's and got similar results. I had to change the cathode bias resistor, and the screen regulator voltage (still in the 275 to 325 volt range) but got over 25 watts from every tube set I tried. I have several hundred assorted NOS tubes in various brand boxes but most appear to be made by GE or Sylvania.
Everything is still packed in boxes since I have moved 1200 miles and won't be unpacked until I build a new lab, but there will be more from the 6HA6/6HB6 in the future since I got a bunch of them.
Keep the screen in the 325 volt range and you can take the plate voltage over 400 volts.
I had variable power supplies on both, but a fixed 6600 ohm OPT. I tweaked the 6BQ5 to it's best performance and simply tried the 6HB6. It could work better at some other conditions.
I settled on 430 volts of B+ because I had a power transformer that could get me there.
There are those that claim it sounds better, and it might if you have a good regulator, but a so-so regulator may make things worse if it's output impedance varies with frequency.
A regulated screen is a good idea in a pentode amp, but you should use cathode bias, or also regulate the bias supply if you regulate the screen supply since the tube current in a pentode is dependent on G1 and G2 voltage, and not so much on the plate voltage.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.