So I want to build an amp with the parts I have aquired based around 4X150A but need some help.

[Onelasttime]

So I have a bunch of odd ball parts that have slowly found their way into my parts bin.

I think I have some place around 10-20 4X150A mostly Jan 7034 NOS in various questionable states. About half of them are still sealed in their Eimace or Jan Packaging NOS. The rest are still sealed int he foil JAN packaging but not in the sealed padded paper bag. I have so many of them I can not realisticly not do a build with them.

I have Nomads high voltage and low voltage boards.

I have a variety of transfromers from Kens Electronics designed for use in CB sweep tube amplifers.

I have dual sockets and chimenys designed for use with 4X150A/D/250 etc....


So in a oerfect world if I was going to spec. a transformer out for this new construstion with center tap and heater etc... What voltage and current should I spec?

I will spec it to use 120V and 240V on the primary since I have both in my garage and my home already.


I want to do this right the first time. I am going slowly. This will be a one and done. Buy once cry once build. I am going to use dual 4x150A tubes on this.


I never planed on doing this build I have just over the last 20 years just had these parts fall into my hands. Most of them where stupid cheap.

Thoughts?


I have nothing else though. I had thought about building a Pride DX300 but with all of these 4x150 tubes I can not not build with them.

 

[nomadradio]

The only real difference between the 4X150 and the 4CX250 is the max operating temperature. All the internal parts are the same. Both versions will happily run hot enough to do damage, even with good airflow. I have seen the 150 used in a Pride. Lasted longer when kept on Low side. Showed normal power on High, but that's risky.

The other way to cope is to use a reduced anode supply, 1700 to 2000 Volts. The Pride's 2400-Volt anode supply is hot-rod territory. An airborne radio using a 150 kept the anode supply below 1500. The Pride was designed to make a wattmeter-watcher salivate, not designed to last a long time. Doesn't mean you can't make a hot rod your dependable daily driver. Just go easy on the throttle. But get carried away and you'll wrap it around a tree.

Quirky trivia. Eimac first introduced the "4X250" as an upgrade of the 150, no "C" in the type number. Had a ceramic ring between anode and screen ring. But the lower "button" where the pins come out was clear glass. Later ones had opaque white glass. Only after the bottom button was also ceramic did it get the "4CX" prefix, best I can tell.

73

 

[Onelasttime]

Thanks!! I was hoping to purchase a Pride DX300 but they always go for stupid money on Ebay!

I am glad I asked because Iw as going to go with 2500 volts. So I will go for the less is more route.

I was going to use your High Voltage and Low Voltage boards in a Pride amp but now I am thinking about using them in this build.

I have at least 2 transformers from Kens Electronics that are 1500V under no load. I am still thinking about going custom though.

What do you think is a safe cushion amp wise? I want to have enough to run 2 tubes with plenty of to spare but also do not want to spend more than I have to. What is a good margin to look for an spec.? A long long time ago when I built my 7GBT amp that I sold and wish I had not I spec.'ed it for what the spec. sheet said 2 tubes would use in class AB1 and added 30%. My thinking was that even with my use of speech compression for SSB the duration of talk time is such that 99% of the time duty cycle would be short enough that even at full rated specification sheet output would not be reached most of the time. Combbined with a 30% buffer even under speech compression whith 30% more voltage and amperage than full AB1 rating that would be more than enough. I only used the amp for a year before I sold it but I never ran into an issue where I felt I needed more transformer.

In this case since you recomend not going hot! If I specified 2000 volts but specified an amperage rating 30% to 50% greater than what 2 tubes would reguire would that be enough buffer to give long life for the transformer and very stable operation for the entire amp?

I would rather have great continious power output than peak power output and reliability. I like to have super stable power output. Normaly I would run voltage higher so I do not get sags but durability is a must. I am not a meter-bater guy. I regret selling my GI7BT tube amp. It was a super reliable beast.

Cooling will not be an issue. Since I am not starting with a Pride amp in this case size is not an issue. Cooling is not an issue. Likewise it is too easy to put the amp in the basement or another room so that the cooling noise is not an issue! I always thought it was silly to limit cooling for noise issues. It is kind of stupid to put limits on a build like it having to fit on your table top as an single box unit.

 

[Naysayer]

get a set of Tetrode Boards, makes it easier and it's a fine circuit. I see that a gentleman in South America somewhere has upgraded the g3sek board and sells them online. His site includes the pcb prints and the material is free.

 

[nomadradio]

Your 1500 Volt transformer will yield about 2100 Volts DC from a bridge rectifier. I sell our Pride HV rectifier/filter board bare with no parts on fleabay. I would recommend 220uf caps to run two tubes, rather than the 100uf parts standard for one tube. The 3-Amp 1N5408 rectifiers are overkill even for two tubes. Cheap overkill is almost never a bad idea.

Shoot me a pm with your mailing addy and I'll send you one for, ah, "evaluation", as they say. The standard "snap-in" capacitors it uses are widely available. Only restriction is size. Max diameter is 30mm.

73