2SC2999 MOD ANALYSIS

[Z-MAN 369]

I did this mod and diodes, not a night & day difference but my recieve is much quieter. When my locals complain about their high noise level, i look down and my needle is at a 1-3db. Worked for me for $12, lol.

 

[giboni]

Old Thread,

Maybe might catch 399's attention I have several 858 radios. Just picked up for $20.

A Washington Base two push buttons 858 chip. Replaced the 1307. Replaced the AMC diode limiter that had been cut. She works !

Still a Golden Screwdriver but getting better fast. What do you think of this transistor

to replace the venerable 2SC1730L.

MPSA18 Low noise very high gain NPN Transistor
TO92 case
Pd 625mw
Vceo 45V
Imax 200ma
Hfe 500-1000 @.1ma to 10ma
Ft 100Mhz
Low Noise 1.5 dBing
High gain and low noise to currents as low as 10 uA, good from low level audio to 33MHz

Estimate at 27 MHZ LN is 1.2

Or how about this circuit using 2 BC347 ? The last picture not the below one.

Right is base. Top is emiter. Bottom is collector.

My purpose is to experiment & see if I can make distant stations a bit louder.

An original real 2sc2999 has only worked for me on 2 Gallaxy 959s that I refurbished.

Other radios. The original was better.

BC347 1x worked in a Uniden PC78. The original was better. Now i'm thinking how about 2.

 

[unit_399]

I think that the MPSA18's AC current gain at 27 mhz (3.70) is far too low for it to be a good replacement for the 2SC1730L ( 40.8 AC gain @ 27 mhz). New China 1730s are available on Ebay and Craigslist. I would try those first.

- 399

 

[giboni]

Thanks a lot !

399 you obviously know how to read the spec sheets of these transistors. What about the above circuit using a pair of BC347 ? It is hard and to match up transistors. The circuit above with resistors matches the BC347's.

Now that I think of it. Pairing 2 2sc1370L !

I have been BURNED a few times on FleaBay. Fake transistors. Some US Sellers with N.O.S. But it comes out to a Buck per Transistor. A bit steep.

Figure you mean Amazon. Not Craigslist.

Sooo many transistors. So little Time LOL.

Ok I'm trying to learn Quick.

"Practically, experiments show that the levels of AC current gain β(ac) and DC current gain β(dc) are more or less equal in their magnitudes and therefore become quite interchangeable. Generally the AC and DC betas tend to have similar magnitudes at lower levels of I(ceo)."

What am I missing ? Ah the published ratings are at the top end of the Mhz parameter?

So what is a simple formula to guess the AC HFE gain at 27 MHZ.

I have a bunch of BC548-549 that I use to make a simple compressor board that works.

The audio power mod I posted in the other thread works by the way.

Getting great audio reports on SSB from Skip stations."trc 457" 858 Chassis.

Eventually will hook up my new used Oscilliscope to check waveforms of the Modulation.

Next purchase. Curve tracer. then a 100 MHZ spectrum analyser LOL !

Best 73s Thanks for taking the time out to respond.

John

 

[Robb]

I think that the MPSA18's AC current gain at 27 mhz (3.70) is far too low for it to be a good replacement for the 2SC1730L ( 40.8 AC gain @ 27 mhz). New China 1730s are available on Ebay and Craigslist. I would try those first.

- 399

I'm a bit gun shy about buying transistors from China. The IC's I've bought (regulator, audio, op amps, etc) from China have all been first-rate quality and were far below eBay's regular market prices compared to the US vendors. But as for final transistors (2sc2166, 2sc1969, etc), all have been bogus. Never buy final or driver transistors from China!!!

There is an American seller on eBay that looks like he has the real NEC brand of 2sc1730L transistors. But am still not certain as to their being the real McCoy/genuine:

http://rover.ebay.com/rover/1/711-5...0001&campid=5336136228&icep_item=291218840849

 

[unit_399]

There is a distributor in Medellin that sells InChange semiconductors. I have bought about a dozen and all of them met their advertised specs. 2 actually exceeded the Hfe spec. Robb, if you can locate a distributor in Calif., get some and give them a try. Unlike rf power transistors, small-signal transistors from China seem to be pretty good. Call them for a distributor 1-

800-828-7177.

- 399

 

[unit_399]

giboni -

From my initial post:
AC Current Gain (hfe) ... is defined as the ratio of the input current to the output current in a device, and depends on the operating frequency. Ft and hfe work together to define the overall AC gain of the transistor at a specific frequency (fo). hfe is calculated using the formula: hfe=Ft/fo. (Where fo is the operating freq.)
Example: For the 2SC1730L at an fo of 27mhz, hfe=1100/27=40.8

 

[giboni]

giboni -

From my initial post:
AC Current Gain (hfe) ... is defined as the ratio of the input current to the output current in a device, and depends on the operating frequency. Ft and hfe work together to define the overall AC gain of the transistor at a specific frequency (fo). hfe is calculated using the formula: hfe=Ft/fo. (Where fo is the operating freq.)
Example: For the 2SC1730L at an fo of 27mhz, hfe=1100/27=40.8

Thanks 399 for the above information. Ok let me find out if I got this right.

Target Transistor is 2N5770.

Monograms Oh Lordy. No simple way to figure Ft. Ft = 900 at 100MHZ

I am totaly Lost. Alright. After looking at 4 different manufacturers data sheets got this.

1800 MHZ

so HFE = 1800/27 = 66.6 So if I got it right.

It seems this Transistor looks like a good substitution for the original Nec 1730L.

Honestly. It really is hit or miss on FleaBay.

Would rather pay .30 cents with shipping than a Dollar plus each on FleaBay and then get disapointed.

Actually-Ripped off.

Best 73s John

3 hours on this. Sooo what sayeth you 399 !

Best 73s John

 

[Robb]

I just bought some 1730's on eBay and will try them out soon . . .

 

[giboni]

I just bought some 1730's on eBay and will try them out soon . . .

Ok its been awhile. Im like a coiled Spring. Did you check them out these 1730's ?

Best John

 

[Robb]

Ok its been awhile. Im like a coiled Spring. Did you check them out these 1730's ?

Best John

Will do it very soon; going to replace both the AM and SSB transistors in a Galaxy 99v . . .

 

[unit_399]

Giboni -
Sorry I didn't get back to you sooner on this. I looked at the specs on the 2N5770, and your calculations are correct. AC current gain is 66.6 @ 27mhz. The problem with this transistor is that it has a spec'd noise figure (NF) of 6db, which is twice as much as the 2SC1730 (NF=3db), so there would be no point using it as it will actually add noise at the receiver front end.

- 399

 

[giboni]

Ah Ha Ha !

Okay. What about BF763 2GH Even higher gain !

800 MHZ 3.9 DB NF
200 MHZ 2.3 DB NF
Seems NF is going down as the frequency gets closer to 27MHZ frequency !!!
27MHZ ?

Thanks for the reply. Any pointers in installing a frequency counter unto the 858 Chassis 2nd generation ?

 

[Robb]

Gain isn't the reaal issue; the 2999 has more gain but isn't as quiet as the 1730. From what 399 said, the 1730 is what makes the 858 chasssis receive better than the 8719 chassis.

 

[giboni]

I have a Uniden Washington base with a Digi-Scan. Noisy and susectible to Splash big time.

Yes. What I am trying to do is find a transistor with low noise and high gain

superior to the 2sc1730L in a TO-92 package if possible. Might not be.

Now that you mention "8719" chassis. Today will "Shotky diode" this Washington Base.

Going to try this Mod. on the Washington 8719.

Please do not make fun of me if I missed something. At least I try !

I like the radio due to the Digi-Scan. I did a PE Mod. Good talker AM and SSB.

with a stock mic. Will try my other Mics soon when I get the Mic adaptors. Too lazy

to swap the 5 pin male to four pin.

Sort of fixed an issue. With a 2sc2166 driving a 2sc1969 would not deadkey past 2 Watts. Switched to a 1306 driving 2sc2078.
Adjusted bias. Then to spec 4 watts.

HERE is My Receive MOD. Tired of being Splashed by Skip Stations.

You know you have to do something when a Guy in Alberta Canada with a Moon

Raker 14 a few hundred whiskeys is bleeding unto the channel your on.

And your ten channels away ! And two thousand miles away !

Many years ago Many. My first solid state radio was the Venerable Cobra 148.

Purchased from CBC International. 455KHZ filterKit & 7.8MHZ filter Kit.

Made a difference. CBC no longer stocks these kits. My 148 was stolen decades ago.

Going to recreate the 455KHZ filter . With new sharper tighter Muratas 2.4 K

Going to try it. Will post whether it works or not on a later date.

I'm going to use the SSB ladder Filter. 7.8MHZ probably 2.4KHZ from a Cobra 138

that was not restorable. As an IF filter on the 8719 Chassis. My Washington.

CBC would not give me the schematic for the 455KHZ filter. Figured it out.

Its on a Bread Board. The Op Amp. preceding the filter is the basic CBC Op Amp

design of the 7.8 & 10.695 Filters. The 138 did not have F2 to canabalize that part.

F2 on a 858 Chassis base is what helps greatly in preventing bleed over. Alas.Mobile

versions were castrated apparently. F2 is a Monolithic Filter 7.8MHZ 2 Pole.

The filter I will try today is a SSB filter that is quite narrow at 7.8MHZ 2.4KHZ I figure.

Most likely 6 or 8 pole? Alright first coffee . A cigarette. Then try this.

It might need another OP Amp stage after the Filter.

Might have to change the 3904 to a 2sc1730. It might not work at all.

Will Post Back ! Keep forgetting to call Uniden. Doubt it if there are any more.


73s John