Actual Measurements of FT-1000D or 3-500Z Amplifier IMD Trash Levels

[w3jn]

This great thread you start Mastah Vu.

When I built my 300B audio amp I used a Heapshit IMD analyzer and a British (can't remember the brand) THD analyzer.  That's a good question, voltage or power.  These instruments measure voltage across a load, which implies that they measure power.  But I guess it all depends on whether they use a 10log scale or a 20log scale.  At any rate, .1% is considered Fine Business for an audio amp and most agree that anything under .5% is undetectable by the human ear.  However, as we know, most receivers (except 51S-1s and SX-117s) have much more dynamic range than the human ear.

Tom Vu the audiophools definitely know about 6550s, but mostly for replacement stock.  Ever price a Tung-Sol 6550?  I scored a quad of them at a hamfest for a quarter a piece, I'm counting on them to fund my kid's college.

Like everything associated with Art Collins that SSB book is very pricey.  I saw one on ebay a few days ago for $100.  I should have invested in real estate in Cedar Rapids; I'm sure the Collins Collectors will discover that next 

73 John

[WA1GFZ]

Yup John, Tom Vu thread ties right in with my receiver disease.
We all need a 1/2 a mil of test equipment in the shack to really know what is going on.

[K1JJ]

Yes, this can be an interesting thread.

Once all of us get on the air and happy with the basic rigs we have, then what's left but to talk -    or later go back to improve upon the rig's performance?

It will be fun putting this new amp on the air for AM too - driven by the clean 5mW from the FT-1000D on AM.  The 1000D's output uses a direct connection to the balanced modulator, with no audio restrictions. If it's anything like the ssb test I made, after the audio frequencies, the "crackle" side trash should drop off into the abyss within a kc or so..  A TX amp is easy to demonstrate whereas a receiver needs a personal visit..

Marv/WC6W has been suggesting using a "feed forward" system for the FT-1000D 200W power amp. He seems to feel it would be all outboard.  ie, sample the 5mw, and feed the 200W module of -32db 3rd in and get 50W of clean -65db+ 3rd  out. I gotta check more into that if it's just a mater of building a "goesinta, goesouta" box.  All I see on the web are complex block diagrams from the ivory castles with no practical circuits or values.  So, it might just come down to starting at 5Mw and going up from there with conventional tubes, etc..

Frank has offered to design up a a pair of 2N3375's pair running a Norton config to get the 5mW to whatever is needed for the 6550 tube.  He thinks that may be the cleanest way.

The thing with this project is that IMD doesn't add linearly. ie, a -55 stage driving a -50 stage is not -52.5, but rather something less than -50.  Each stage must be at least -10db cleaner than the next one.  The real IMD problem maker will be the final tube that needs to generate power. I hope to add a cathode NFB resistor there AND the highest NFB loop around it to the driver I can get away with. If the final tube will do -35db spec alone, then adding -20db will bring the final up to the desired -55db IMD goal.

It will be fun starting from low level and proofing out each stage. I need to set up a 2 tone generator and directional coupler for numbers tests.  But first more planning and thinking to do.

T

[WA1GFZ]

Tom look at the norton schematic. All you have to do is change the emitter resistors to get the resting current you want. 3375 want to run about 100 to 120 ma. each.
TO5s start getting pretty warm at 60 ma. The 3375 is a stud mounter device 10-32 thread. 3632 is another good one that does more power.

[K1JJ]

Tom look at the norton schematic. All you have to do is change the emitter resistors to get the resting current you want. 3375 want to run about 100 to 120 ma. each.
TO5s start getting pretty warm at 60 ma. The 3375 is a stud mounter device 10-32 thread. 3632 is another good one that does more power.

Frank,
Is there an advantage to using a 3.8 mhz resonant tank(s) with this Norton circuit or do you use resistors or ferrite transformers and make it broadbanded?  Maybe an output tank wud help cuz the Norton may be 20' or more away from the big linear input, I dunno. I see your info used broadband transformers in and out.

BTW, what schematic would you suggest I build? Maybe you sent me one, but all I have is the multi page article on Norton amps...

I'm not sure yet if this linear amp will be a mono band 75M unit or will go form 160-20M.  It all depends upon the feedback used and other factors.

T

[WA1GFZ]

I would stay with the transformers for broad band feedback and impedance control. You could hang a low pass after it. Harmonic energy should be low but a low pass wouldn hurt. Check the aritcle again there are schematics. I can resend if you need me to. I did the 10 dB gain push pull with 2N5109s. That is the only one I tried so far.
The next logical power level 1 watt or so would be an MRF type driver transistor like a MRF466 or MRF 433. BTW Pete SOV uses a CTI driver 2 stages class A in his Rig.
The bias had to be cut back because it over heated but worked fine. Check out the CTI thing. TO220 transistors. MRF 475 and 472 if I remember. They also have a couple others worth checking that were clean. The 2N3375 is older but should work.
The trick is to use a device with high Ft. The 2N5109 is 1800 MHz Ft if I remember.
The gain of the stage is set by the transformer ratios. there should be a chart.