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Old 28th March 2013, 03:20 AM   #51
Magz is offline Magz  United States
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Quote:
Originally Posted by iko View Post
You plan to run two of those regulators in parallel? That will be interesting.
Rod actually recommended it to me, so no worries. I just need to make sure they have mucho heat sinking.
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Old 28th March 2013, 03:27 AM   #52
Magz is offline Magz  United States
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Since we're talking power supplies, here's the PSUD for the 6E5P driver supply (V2 in the schematic). 1mV ripple.
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File Type: jpg 833 Driver PSUD.jpg (183.1 KB, 1194 views)

Last edited by Magz; 28th March 2013 at 03:50 AM.
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Old 28th March 2013, 03:32 AM   #53
Magz is offline Magz  United States
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And here's the PSUD for the 833 B+...


a little underdamped, perhaps, but not too much. Should be nice and fast. 12mV ripple.
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File Type: jpg 833 HT Supply PSUD.jpg (165.9 KB, 1175 views)

Last edited by Magz; 28th March 2013 at 03:50 AM.
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Old 28th March 2013, 03:42 AM   #54
rmb is offline rmb  United States
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Tubelab.com: Don't expect a lot of glow from a 3B28. You will get a blue glow from the 866A (the mercury counterpart). If you look carefully (BE CAREFUL, HIGH VOLTAGE!), what glow you see is between the plate and the filament. Preheating the filament before applying HT is mandatory.

There was a comment about the C3J thyratron. If that tube has a PIV of 1200 volts, the RMS AC supply must not exceed 850 volts. Hopefully, you won't be "pushing your luck" using a 800 volt transformer. The grid controlled regulator/control is a nice concept...thyratrons are sort of like SCR's, once they fire, they conduct until the AC supply goes through almost zero crossing. But the grid control can deal with the conduction cycle and other nice things...

Last but not least is the 833A. Nice tube. Still used in some older broadcast gear still in service. The 833A was used (in a pair) as a class B modulator in older Gates, RCA, and other 1 kW am transmitters. Two of these (in parallel) were used as RF final amplifiers at the 1 kw level. The filament transformers (secondary voltage 10 V at 20 A for a pair of 833's) was center tapped and the dc return circuits were taken off the center tap. Fixed bias was normally used with this tube to set the operating point (and protect it).
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Old 28th March 2013, 03:47 AM   #55
iko is offline iko  Canada
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Quote:
Originally Posted by Magz View Post
Rod actually recommended it to me, so no worries. I just need to make sure they have mucho heat sinking.
Sounds good then.
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Old 28th March 2013, 04:07 AM   #56
Magz is offline Magz  United States
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My main worry about the single chassis design is hum from the 10A filament supply, even with the AC part 20"or so away from the signal circuitry. I'm kicking around the idea of a separate small steel chassis just for the filament trannie, chokes and caps, with an umbilical connection to the main chassis. It would also give me a lot more room in the main chassis for all the rest of the parts.

Stay tuned.
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Old 28th March 2013, 04:22 PM   #57
rmb is offline rmb  United States
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Magz: Suggest using a cooling fan and the heat radiating connectors on the plate and grid connections to the 833A. The ceramic filament "socket" supports the tube. Avoid mechanical stress to any of the connections to the 833A to avoid damaging the glass to metal seals. The 833A is installed filament connections down, with air directed to the top of the tube to cool it in CCS (continuous commercial service) use. This tube is sensitive to filament voltage and in broadcast use, the tube wants 10 volts on the filament, measured at the tube. Since audio output use is essentially equivalent to continuous broadcast operation, use the CCS ratings to maximize tube life.

In the older tube broadcast transmitters using the 833A, the heavy iron components are located at the bottom of the cabinet (plate transformer, HT choke, modulation transformer, modulation choke, etc.) and the power components (modulator, RF final) are located near the top of the cabinet (on separate chassis assemblies). The cooling fan is located on top of the cabinet to force air on the power tubes. Filament transformers for the power tubes were located on the cabinet side walls, and a variac typically was used to fine adjust the filament voltage.

If you want a tube power supply with a bridge rectifier, four 3B28 or 866A will work with plate current on the order of 250 mA. In broadcast use, the 8008XE or the 575A was used. I liked the 575A with its higher peak inverse voltage and less prone to arc back. Virtually all the tube broadcast transmitters in the 1 kW range were powered off standard 220 volt single phase AC (same power that runs your electric stove, central air conditioning, well pump, etc.).

Did you think of locating a metal cabinet (approx. 36-48 in high) equipped with standard 19 in rack rails that accommodate the power supply and audio subassemblies "under one roof"? The older Bud cabinets had the rack rails in front and a door in the back, which could be closed and keep people and pets away from the HT...
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Old 28th March 2013, 04:38 PM   #58
hpeter is offline hpeter  Europe
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Quote:
Originally Posted by tubelab.com View Post
Breadboard and test everything before thinking about the chassis. With 100 watts of heater power in the 833A hum will be a problem. I HAD to use DC for the filament. I would get audible hum in the speakers with ONLY the filament transformer switched on, NO B+. Moving things around did not help. I needed a big fat bridge some big caps, and a choke wound with something resembling welding cable!
Why not use these instead of heavy iron? exists also types with active pfc
Click the image to open in full size.
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Old 28th March 2013, 04:38 PM   #59
Magz is offline Magz  United States
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Originally Posted by rmb View Post
Magz: Suggest using a cooling fan and the heat radiating connectors on the plate and grid connections to the 833A. The ceramic filament "socket" supports the tube. Avoid mechanical stress to any of the connections to the 833A to avoid damaging the glass to metal seals. The 833A is installed filament connections down, with air directed to the top of the tube to cool it in CCS (continuous commercial service) use. This tube is sensitive to filament voltage and in broadcast use, the tube wants 10 volts on the filament, measured at the tube. Since audio output use is essentially equivalent to continuous broadcast operation, use the CCS ratings to maximize tube life.

In the older tube broadcast transmitters using the 833A, the heavy iron components are located at the bottom of the cabinet (plate transformer, HT choke, modulation transformer, modulation choke, etc.) and the power components (modulator, RF final) are located near the top of the cabinet (on separate chassis assemblies). The cooling fan is located on top of the cabinet to force air on the power tubes. Filament transformers for the power tubes were located on the cabinet side walls, and a variac typically was used to fine adjust the filament voltage.

If you want a tube power supply with a bridge rectifier, four 3B28 or 866A will work with plate current on the order of 250 mA. In broadcast use, the 8008XE or the 575A was used. I liked the 575A with its higher peak inverse voltage and less prone to arc back. Virtually all the tube broadcast transmitters in the 1 kW range were powered off standard 220 volt single phase AC (same power that runs your electric stove, central air conditioning, well pump, etc.).

Did you think of locating a metal cabinet (approx. 36-48 in high) equipped with standard 19 in rack rails that accommodate the power supply and audio subassemblies "under one roof"? The older Bud cabinets had the rack rails in front and a door in the back, which could be closed and keep people and pets away from the HT...
I have finned top caps for the 833, and plan to have a small fan (33cfm DC brushless) for cooling. I have read that too much cooling is detrimental to performance, and the Penta 833C has a maximum cfm spec of 40. What they used to do in some cases was to use the warmed air from the power supply chassis to cool the 833 to prevent over-cooling. I can do that by placing a fan under the 833 and sucking the warmed air from the chassis and directing it up and around the 833, which will be surrounded by a borosilicate glass tube.

For rectification I'm going with SiC schottky diodes, four in series per leg of the bridge, 4800PIV. My supply is choke input with a soft start circuit, so there will be a relatively smooth current draw from the supply.

A 3-4 foot tall cabinet will not meet WAF. I need to keep it to max 19"x23"x4.25".

Last edited by Magz; 28th March 2013 at 04:40 PM.
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Old 28th March 2013, 04:52 PM   #60
hpeter is offline hpeter  Europe
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Quote:
Originally Posted by rmb View Post
There was a comment about the C3J thyratron. If that tube has a PIV of 1200 volts, the RMS AC supply must not exceed 850 volts. Hopefully, you won't be "pushing your luck" using a 800 volt transformer. The grid controlled regulator/control is a nice concept...thyratrons are sort of like SCR's, once they fire, they conduct until the AC supply goes through almost zero crossing. But the grid control can deal with the conduction cycle and other nice things...
yes i did mistake in concept, thanks to the zero cross circuit it would never fire thyratrons.
i like idea of having a full regulated anode supply (with tubes)
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