JOHNSON T-BOLT..WHATCA THINK...?

[ve6pg]

...hey, from tim...last time i saw a johnson thunderbolt, it was sitting outside this guy's house, on garbage day...musta been around, 1973....gutted...sad sight...
..anyway, i  *might* have a chance a getting a t-bolt...need to know ur thoughts on this fella...pair of 4-400s, sounds kinda ok fine to me.
 i think the drive is rather low, being that i think the box is grid drive.
..so, i am looking fer input as to the box..ur thoughts, suggestions, etc...tnx...tim...sk...

[Pete, WA2CWA]

If you're thinking of using it on AM, a Valiant will provide almost as much output. High voltage supply is low for the 4-400's. Works OK on SSB. Weighs a ton. No 160.

[Jerry-n5ugw]

Jeff, W0XV uses one with  ranger on 3885 down south. He punches a big whole with the audio. Ranger has mods.

[The Slab Bacon]

If you are planning to buy a t-bolt, be sure that a hernia truss comes with the deal.They are just the epitome of a boatanchor. For AM they are piss weak and not worth the bother!! 150 lbs for 150w of am carrier kinda aint worth the bother.
(I have one) But they are ok if you want it as a collectable.

                                                     The Slab Bacon

[ve6pg]

...i thought the t-bolt was an amp with more output...i know the courier is about 150, fer am....a pair of 4-400s, not grounded grid...only 150watts?...this is the same final as the desk kilowatt is it not?...tim...sk..

[WD8BIL]

Hi Tim,

If its such a deal ya can't pass up......

Rework it for class c and build a modulator for it.
A pair of 4-400s will kick butt !

[wa2dtw]

Bud
That sounds like a great project (i.e. converting to class C and building a modulator).  Would higher plate voltage on the 4-400A's be needed, and could one use the same power supply for the 4-400A's and the modulator?  Do you know if there is a schematic floating around someplace?
I have a T-bolt paired with the Ranger.  Using Timtron's method for reducing the output power of the Ranger (i.e. low B+ voltage on the plate of the 6146).  Works fine.  I think I am getting around 250 watts of AM carrier out of it. (as opposed to 150 for the Valiant).  I keep it parked on 3885.  The lack of 160 is a real disadvantage. 
73
Steve WA2DTW

[k7yoo]

Building a modulator for it would be a very bad idea. The tank circuit is barely heavier than a Viking 2. Look at the tank in the desk KW and you will see that it is rated to handle 100% modulated full carrier out. To get an idea of the capabilities of the T-bolt take the dead carrier output and divide by 3+/-. This is how much AM carrier it will handle. All the 2KW PEP advertising they gave them was pure hype. The dead carrier max power is what the amp will do on audio peaks.

[K1JJ]

Hi Tim,

I understand the plate transformer in the T-Bolt is a weak link. Even the one I got years ago had a blown xfmr right from the start.  I built a separate supply for it and gutted the original suppy. That made the T-Bolt EZ to carry around....

Yes, I remember the tank circuit to be very light duty - especially becuz of that small roller inductor. After I put higher than stock voltage to the unit with the new HB supply, the roller developed intermitant hot spots and crapped out. I think the HB supply was about 3kv.  I've had 4KV on homebrew 4-400A linears before with no problems, but the T-Bolt is designed for about 2KV.

If it were mine, I'd keep it stock and be happy with what it is.    THEN, collect the parts and build up your own class C, plate modulated 813's or 4-400 AM rig...   You know what they say about trying to make a silk big-rig from a sow's ear...

T

[The Slab Bacon]

the big problem with the T-bolt is the low plate voltage. (2000v) The 400s are yawning at that voltage. But............the plate tank coil and cap arent good for any more. the roller inductor is weak and wimpy and the plate tuning cap is spaced too close to handle any more voltage. About 600w PEP is all they are good for, which works out to about 150w am carrier. I was gonna try to modulate mine years ago, but one good look at the plate tank changed my mind. the power supply is indestructable, but the voltage is toooooo low.

IIRC, the 2000w rating was PEP DC inpoot.

Why reinvent the wheel?? Get (or build) a real amp!

                                                                        The Slab Bacon

[Pete, WA2CWA]

I originally had two, got rid of one at Dayton last year, that were used at Bell Labs in some laser lab. On the air testing several years ago, side-by-side Valiant and Ranger driving the T-bolt, receiving end saw little difference in carrier strength. As others have pointed out, the tank circuit is not very manly and will arc all over the place if you try to squeeze additional RF out of it in the AM mode. On SSB, it is more tolerable, which is where I use mine today. The CE 100V and the Icom 756 PRO II drive it fine.

[w1vtp]

...i thought the t-bolt was an amp with more output...i know the courier is about 150, fer am....a pair of 4-400s, not grounded grid...only 150watts?...this is the same final as the desk kilowatt is it not?...tim...sk..

  Emphasis mine

Are we talking input power or output power?  I have a Courier and I run it at 70 watts carrier output.  That allows for 200 - 300 watts PEP on audio peaks with more than 100% mod on the positive peaks.  To run a Courier at 150 watts carrier output implies at least 600 watts of PEP capability which simply is not available on a Courier.

Regards, Al

http://homepage.fcgnetworks.net/w1vtp/station/w1vtp_qrz-rs.jpg

[Pete, WA2CWA]

Are we talking input power or output power?  I have a Courier and I run it at 70 watts carrier output.  That allows for 200 - 300 watts PEP on audio peaks with more than 100% mod on the positive peaks.  To run a Courier at 150 watts carrier output implies at least 600 watts of PEP capability which simply is not available on a Courier.

Regards, Al

http://homepage.fcgnetworks.net/w1vtp/station/w1vtp_qrz-rs.jpg

When I run the Courier (with 572B's) being driven by the Icom IC756 PRO II or the IC-7000, both with their "low-level AM Modulation", I generally run the Courier at about 110 or 120 watts RF output. When you modulate the exciter, the plate current in the  linear actually decreases due to the ALC action in the exciter.

[Opcom]

T-bolt was OK, but weighed a ton. Mine had an outboard power transformer because the original had fried. It ran about 500W output maximum and was easily driven by a few watts. I ran it with one 4-400 for a while and didn't notice much difference, it was easy on the tubes.. I did not like it on AM with 100W carrier due to poor cooling.

[N3DRB The Derb]

they are marvelous looking, but the scrotes on them are tiny. I do believe a Gonset 201 with 572B's will kick it's ass or come very close.