[L0rdGwyn]

Another connoisseur of fine tantalum plate transmitter tubes I see

My collection of 4E27A tubes so far:

Very nice, any plans to build with them? I have a batch of 3C24 and now the big brother HK54. Tracked down some NOS Eimac heat-dissipating plate / grid caps as well, could go in a positive grid biased A2 design some day, but who knows!

 

[A2029]

Very nice, any plans to build with them? I have a batch of 3C24 and now the big brother HK54. Tracked down some NOS Eimac heat-dissipating plate / grid caps as well, could go in a positive grid biased A2 design some day, but who knows!

Definitely hope to do a build with them at some point, likely not for me to keep though as I already have a different personal speaker amp to keep. Only one tube per channel would be needed with these 4E27A as they have crazy high 125W max dissipation. I was originally thinking of a voltage between 1000-1200V, but I may end up sticking to something more conservative like 750-800V. One problem is the top cap that I don't feel very comfortable leaving exposed even with *only* 750V on them. I'll be looking to custom CNC some top caps that are electrically insulated with at least 3-5KV of electrical insulation capacity in case someone accidentally touches the top cap.

A1 plate curves for the triode stapped 4E27A are very nice, which got me started accumulating all of these.

 

[L0rdGwyn]

Definitely hope to do a build with them at some point, likely not for me to keep though as I already have a different personal speaker amp to keep. Only one tube per channel would be needed with these 4E27A as they have crazy high 125W max dissipation. I was originally thinking of a voltage between 1000-1200V, but I may end up sticking to something more conservative like 750-800V. One problem is the top cap that I don't feel very comfortable leaving exposed even with *only* 750V on them. I'll be looking to custom CNC some top caps that are electrically insulated with at least 3-5KV of electrical insulation capacity in case someone accidentally touches the top cap.

A1 plate curves for the triode stapped 4E27A are very nice, which got me started accumulating all of these.

Awesome, nice curves! Would be a beast of an amp in A1. Any idea of the plate resistance triode-strapped? Out and about or I might've eyeballed it. I hear you on the caps, I would be looking at ~300V exposed with the 3C24. I thought about insulating them as well, but figured the insulating material would need to posess a high thermal conductivity to maintain the cap's heatsinking function. I didn't look into it deeply, once I found the Eimac caps I thought I would encase the tubes in glass with ventilation, so no touchy. Who knows if it will ever happen but it's fun to hoard tubes and fantasize

 

[Zachik]

Got some more crazy transmitting triodes yesterday, Gammatron HK54. These monsters have a 50W plate dissipation and a 5V / 5A filament, safe to say you could cook / pulverize an egg on these babies when biased to max plate dissipation.

My collection of 4E27A tubes so far:

I am gonna report you guys to the DOE

 

[A2029]

Awesome, nice curves! Would be a beast of an amp in A1. Any idea of the plate resistance triode-strapped? Out and about or I might've eyeballed it. I hear you on the caps, I would be looking at ~300V exposed with the 3C24. I thought about insulating them as well, but figured the insulating material would need to posess a high thermal conductivity to maintain the cap's heatsinking function. I didn't look into it deeply, once I found the Eimac caps I thought I would encase the tubes in glass with ventilation, so no touchy. Who knows if it will ever happen but it's fun to hoard tubes and fantasize

I believe plate resistance in the 1200 ohm range, so a 5K transformer would work well.

Here is my idea for the top cap, crudely drawn in paint in about 10 seconds:

Black is aluminum tubes, white would be high heat thermal epoxy in between the tubes. Innermost black tube could be copper instead of aluminum, and it gets soldered directly to a high heat, high voltage insulated copper wire. A set screw from the side holds the inner copper tube to the anode pin, and a removable plug goes in the set screw hole. The outer aluminum tube can be anodized color of choice (anodization also increases the electrical insulation), and the outermost tube could be the tallest so that the top area over the inner copper and aluminum tubes could be filled with thermal epoxy.

I may just go with glass surrounding the whole tube eventually though, not sure yet.

 

[Galapac]

I believe plate resistance in the 1200 ohm range, so a 5K transformer would work well.

Here is my idea for the top cap, crudely drawn in paint in about 10 seconds:

Black is aluminum tubes, white would be high heat thermal epoxy in between the tubes. Innermost black tube could be copper instead of aluminum, and it gets soldered directly to a high heat, high voltage insulated copper wire. A set screw from the side holds the inner copper tube to the anode pin, and a removable plug goes in the set screw hole. The outer aluminum tube can be anodized color of choice (anodization also increases the electrical insulation), and the outermost tube could be the tallest so that the top area over the inner copper and aluminum tubes could be filled with thermal epoxy.

I may just go with glass surrounding the whole tube eventually though, not sure yet.

 

[L0rdGwyn]

I believe plate resistance in the 1200 ohm range, so a 5K transformer would work well.

Here is my idea for the top cap, crudely drawn in paint in about 10 seconds:

Black is aluminum tubes, white would be high heat thermal epoxy in between the tubes. Innermost black tube could be copper instead of aluminum, and it gets soldered directly to a high heat, high voltage insulated copper wire. A set screw from the side holds the inner copper tube to the anode pin, and a removable plug goes in the set screw hole. The outer aluminum tube can be anodized color of choice (anodization also increases the electrical insulation), and the outermost tube could be the tallest so that the top area over the inner copper and aluminum tubes could be filled with thermal epoxy.

I may just go with glass surrounding the whole tube eventually though, not sure yet.

Thought that was an optical illusion when I glanced at my phone awesome, I would love to see it! I'd imagine the surface area would be high, another plus. Bet you could sell these to transmitting tube heads on diyAudio.

Here is a 3C24 with the NOS Eimac HR2 caps.



These would require NFB, not unlike my 801A design. Since these tubes would have a positive grid bias point, an interesting way to implement them is to choke load a direct-coupled cathode follower to handle the negative grid swings, removing the need for a negative bias supply. In my mind's eye the tubes are encased in a glass cylinder with a perforated lid, I think that would look nice.

 

[bcowen]

One problem is the top cap that I don't feel very comfortable leaving exposed even with *only* 750V on them. I'll be looking to custom CNC some top caps that are electrically insulated with at least 3-5KV of electrical insulation capacity in case someone accidentally touches the top cap.

I vote for @UntilThen to get the first amp, then touch the top caps (unprotected) and let us know if it hurts.

 

[leftside]

I vote for @UntilThen to get the first amp, then touch the top caps (unprotected) and let us know if it hurts.

With his tongue haha

 

[UntilThen]

I heard my name mentioned. Did I win a prize? Or the amp...,,

 

[bcowen]

With his tongue haha

LOL! Yeah, that too. And with bare feet on a wet floor.

 

[bcowen]

I heard my name mentioned. Did I win a prize? Or the amp...,,

Yes. But 'win' is a subjective term in this case.

 

[L0rdGwyn]

Finished the 841 amp.

Here is the circuit. Switch in the middle changes the turns ratio of the output transformers to accommodate different headphone impedances. Wiring that baby was a real joy.



Here it is without the tubes. Volume knob on the left, impedance switch in the center.



And with the 841 globes.

 

[bcowen]

Finished the 841 amp.

Here is the circuit. Switch in the middle changes the turns ratio of the output transformers to accommodate different headphone impedances. Wiring that baby was a real joy.



Here it is without the tubes. Volume knob on the left, impedance switch in the center.



And with the 841 globes.

Way impressive! How does it sound?

 

[L0rdGwyn]

Way impressive! How does it sound?

It sounds phenomenal! The bass is very deep, big soundstage and excellent transparency. Sorry had to finish that nail-biter of a game, pictures aren't my best work either lol. Disappointing loss but great season for the Browns.