Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: Prev 1 [2]   Go Down
  Print  
Author Topic: HF amp using 1625 tubes  (Read 14573 times)
KC5HMC
Member

Posts: 90




Ignore
« Reply #15 on: October 24, 2008, 02:44:18 PM »

It even mentions that you have to mod the tubes as mentioned by K4DPK and N2EY.It says you first remove the base by applying heat from a large torch, seperate the cathode and beam-plate leads, and reinstall the base using Tube-base cement. What can I use as a sub for the cement?
Logged
VE3LYX
Member

Posts: 156




Ignore
« Reply #16 on: February 10, 2013, 07:23:41 PM »

I just bought 10 of them NOS. I needed one for my ARC5 T18 . Thought also about building a quad four.Grounded grid is no good here. The homebrew Am stuff here wouldnt have the suds to drive one. it will have to be a grid driven amp. Have built a few , even a parallel 6l6 amp that is sitting be side me right now. Other then top plate lead shouldnt be much difference if any circuit wise.
Half the gird bias for two so 1/4 for four I guess. Seperate parasistic suppressors for all with a common tie point. Make a Rf plate choke to handle all 4 and a gimmick cap per tube for neutralization issues.  They cant be all bad. The Arc 5 has only two tubes ahead of them . A vfo and a buffer I guess of sorts. There is a parallel pair of 807 in the ARRL book. Specs are not a whole lot different then a plain jane 6146 except I dont think they like higher freqs like the 6146. A few years late but mirror cement for replacing automotive mirrors that are glued to the windshield work pefectly and has no resisdue like some of the other popular fixes do. I use it for all my loose tubes.
Don VE3LYX
Logged
G3RZP
Member

Posts: 4830




Ignore
« Reply #17 on: February 11, 2013, 01:35:07 AM »

Parallel tubes need the same grid bias. But if the tubes are in Class C, then the grid leak needs to be one quarter of that which you would use for one tube. The ARC5 T18 used a 1626 triode oscillator to drive the 1625s - the other tube was a magic eye for frequency checking.

For a linear amplifier, I would go for grounded cathode swamped grid as WB6BYU suggests, although I would go for a separate bias pot for each tube, as they don't necessarily match.
Logged
N2EY
Member

Posts: 3909




Ignore
« Reply #18 on: February 11, 2013, 01:33:20 PM »

Thought also about building a quad four.

Think carefully about that. Getting 4 1625s to be stable in grounded-cathode is not going to be easy. It can be done but you have to be very careful with layout, bypassing, shielding, and neutralizing. If all you want is 160, 75 and maybe 40, you may be OK. Note that the pi-net output values will include lots of C and not much L.

Half the gird bias for two so 1/4 for four I guess.

No! Same bias voltage, four times the current.

Seperate parasistic suppressors for all with a common tie point. Make a Rf plate choke to handle all 4 and a gimmick cap per tube for neutralization issues. 

No, one big neutralizer for all 4. Not a gimmick, either.

They cant be all bad. The Arc 5 has only two tubes ahead of them . A vfo and a buffer I guess of sorts.

The ARC-5 uses a 1626 power oscillator to drive a pair of 1625s. No buffer, though many hams modified them to include a buffer because they can chirp and FM pretty bad if you don't.

There is a parallel pair of 807 in the ARRL book. Specs are not a whole lot different then a plain jane 6146 except I dont think they like higher freqs like the 6146.

Max power input of a 6146B is 120 watts. Max power input of a 6146 is 90 watts. Max power input of an 807 or 1625 is 75 watts. (Class C maximum ICAS ratings).

Hams used to beat the tar out of 1625s because they could be had surplus in almost unlimited quantities for 19 cents each. That's not the case any more, and those old bottles should be treated with more respect.

btw, in AM linear a quad of 1625s is only good for about 50 watts carrier output.

73 de Jim, N2EY
Logged
G3RZP
Member

Posts: 4830




Ignore
« Reply #19 on: February 12, 2013, 06:53:06 AM »

1956 ARRL handbook has a design (p.303 et seq)  from QST for April 1954. 2 paralleled 1625s in push pull with 2 more. On page 306, it has the 4 off 1625 parallelled grounded grid amp from QST June 1955.
Logged
N2EY
Member

Posts: 3909




Ignore
« Reply #20 on: February 12, 2013, 11:11:14 AM »

1956 ARRL handbook has a design (p.303 et seq)  from QST for April 1954. 2 paralleled 1625s in push pull with 2 more.

A decent design. Lots of parts for the power level - and not a pi-net.

On page 306, it has the 4 off 1625 parallelled grounded grid amp from QST June 1955.

Which became the P&H L-400.

Note that the design uses modified 1625s. Only some brands can be modified to separate the beam-forming plates from the cathode.

Note too that the design exceeds tube ratings quite a bit....

73 de Jim, N2EY
Logged
G3RZP
Member

Posts: 4830




Ignore
« Reply #21 on: February 13, 2013, 03:09:50 AM »


>Note too that the design exceeds tube ratings quite a bit....<

But, Jim, 1625s and 807s are tough babies, so on SSB, they'll take it. Just don't tune up with single tone for too long. Or run SSTV, RTTY or AM.

I don't think the audiophools have discovered them yet....
Logged
VE3LYX
Member

Posts: 156




Ignore
« Reply #22 on: February 15, 2013, 07:25:02 PM »

Might be difficult. Well I hope so! Otherwise it would hardly be fun.
Mod the tubes? That is only for grounded grid. Grounded grid requires a pretty stout exciter to drive it. I dont have that kind of power in my exciter.
Don VE3LYX
Logged
WB3COB
Member

Posts: 6




Ignore
« Reply #23 on: February 19, 2013, 05:34:16 AM »

   1625 amplifier, 150 watts QST April 1961 "Surplus tubes + an Old TV Set = 150- Watt Amplifier by McCoy. 
  The1625 is a good tube, but needs a base shield.  Old soup can works well with vent holes cut in the bottom for air circulation and spade bolts to mount the can.  Millen used to make the base shields.  Salvaged two from an old low power AM brodcast band Gates transmitter.  I have also seen them on the old Millen exciters and larger Gates AM broadcast transmitters from the
early 1960's.  BC-1T is an example.  Also the ARC-5 transmitters.
Trust me, use a base shield.  It will save you a world of problems.
Also, use a parasitic supperssor.   2 Watt 47 Ohm carbon resistor with 6 to 8 turns of # 20 wire wrapped on resistor body and even spaced. 
   I have used 1625 up to 18 MHz.,  with no problems.  But using the above listed precautions. 
    QST November 1972 shows a nice 14 / 21 MHz transmitter
using 1625 as well.

73's,

WB3COB
 
Logged
KH2G
Member

Posts: 324




Ignore
« Reply #24 on: March 09, 2013, 03:19:17 PM »

If you can find the schematic or a live ARC-5 Command transmitter, they used 2 in them and the sockets were ideal as they have the shielding built in -hi
73
Dick KH2G
Logged
W6OVP
Member

Posts: 2




Ignore
« Reply #25 on: July 19, 2014, 07:04:11 PM »

About 1959 I built a linear using 4 1625's from a QST design.

It was easy to open the base of each 1625 by taking a short piece of rat tail file and putting it in an electric drill, then spinning it to cut a slot in the base. From there it was not difficult to move the tube wires around using a long tweezer and a soldering iron.

In addition to modifying the tube pin wiring, I designed and built the high voltage plate xfrmr using laminations from several old TV power transformers. The design formulas and technique came from a little booklet put out by the US Printing Office, which used to have all sorts of good pubications like that for just a few pennies each.  Also designed and built the filament transformer, and the HV power supply choke, both from old TV transformers which were abundant.

To wind the wire I had an old Jewelers lathe and added a manual crank. Then made a temporary transformer core from a small piece of wood and drilled a hole through the middle for mounting on the lathe. A custom cardboard spool to hold the wire would be taped to it and the wire wound into place in that spool by turning the crank, and counting. The finished result was HEAVY! as are all plate transformers.

Mounted it all on a chassis attached to a 19" aluminum rack panel, and mounted the finished result in a short cabinet. It worked good. And I learned a LOT from doing it.
Logged
G3RZP
Member

Posts: 4830




Ignore
« Reply #26 on: July 20, 2014, 04:29:27 AM »

Back in 1963, I ran an 807 for quite a time with about 1600 volts on the plate, 600 on the screen and around minus 200 or so on the grid. Drove it from a 6L6 running around 12 watts input. Glowed red if you held the key down, but it was in extreme Class C and ran about 250 watts DC input and around 180 or so watts out on 40m. It was a WW2 tube, so wasn't exactly new then. Incidentally, the British made 807s with a white ceramic base never seemed as efficient as the RCA ones.

One interesting variant that was uncommon was the 8018, which according to my father, was selected for full ratings at 112 MHz in an RAF transmitter. He instructed on that tx, but it was never very common or successful.

They would take a lot of misuse.......
Logged
K8AXW
Member

Posts: 3956




Ignore
« Reply #27 on: July 20, 2014, 08:58:31 AM »

HMC:  Since many of the construction articles in the Handbook came from articles published in QST, would you take a few minutes to list the names of the Handbook articles?

I'm an avid builder.....and although I certainly don't build everything I read about, I still enjoy reading about items that others have built.
Logged
Pages: Prev 1 [2]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!