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Author Topic: Dentron Amplifiers  (Read 10194 times)
W8JX
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Posts: 5364




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« Reply #15 on: February 23, 2011, 07:00:53 PM »

Apparently you don't remember the GLS1000? Or the MLA1200? Or the 10-160 with 811As? All of them were made to a specific price segment, and as such had some less than stellar parts.

Oh but I do and I also remember the GLA (it was not a S) 1000B and C which were much improved (for a sweep tube amp). As far as 160L, back then 572's were pricey and the 811 version was simply a lower plate voltage amp version. ANd while I have never contested with my Dentron QRO, I have rag chewed for 6 hours and more using it and it has never fussed about it.
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K7PEH
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« Reply #16 on: February 23, 2011, 07:01:33 PM »

Reading all these comments about the Dentron amps is interesting.  To me, it is sort of like reading about some historical thing since I have a huge gap in my ham radio experience.  Was a novice back in the mid-1960s and then left the hobby until I returned in 2004.  Therefore, all that history, the coming of age of companies such as Ameritron, Dentron, Alpha, and so on came about after I left the hobby and were almost dead (in their original form) when I returned to the hobby.  I know that Ameritron and Alpha amps are still around but not with the original companies.

I built a dual 811 amplifier when I was in high-school and college -- right out of the ARRL HB of the day (I think 1963 or 1964).  It worked great but I never did really use it on the air.  For one thing, I was not licensed to use it and another it was only about two months after I finished the amp that I retired my station.  Just got too busy with class work and chasing girls.  I have a photo of that Novice station I had in college with the homebrew 811 amp taking up most of the space on my www.k7peh.com web page (just page down to Novice Station link).
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K1JHS
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« Reply #17 on: February 26, 2011, 05:20:53 AM »

Well my MLA-2500A uses the 8875s and it has managed to work for some 30 plus years so there is no question as to it's reliability (caveat, those may not be the original tubes). The only drawback is the tubes have been orphaned and I will some day have to have the amp converted to something else but from what I can see that may happen to alot of tubes moving into the future. I feel solid state, while quite good, is STILL not ready for prime time when it comes to RF power amps. If tubes can still be made reliably and cheaply there is no reason for a tube amp to not be used and rebuilt where needed for 100 years or more. The sweep tube amps as has been stated before were made when the tubes were dirt cheap and purchasable in some grocery stores (I remember 2 of them as a kid that had both testers and tubes for sale) ! Of course that was also back when I had a Lafeyette store to ride my bicycle to. I wonder when Eimac will just stop making the 8877? Also what happen to Svetlana? I recall reading they made 8874's but I have yet to see any marked for sale anyplace. Did they actually make them?
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W3HKK
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« Reply #18 on: February 28, 2011, 06:24:36 AM »

I used a Clipperton L in heavy contesting on all bands for 15 years before selling it ( deed restrictions at new qth)  Worked flawlessly and the 572Bs lasted a reasonable 4-5 years considering ther workload.  At the end  a couple of the parisitic chokes on 10m were blistered andthe solder crystallized, probably from  improper tuning as I moved around the bands and changed frequencies on the fly.

Neat looking rig. 

A friend brought in a MLA2500 for me to test and it was  quieter than my L and  had the original tube.  Very impressive amp once you get around the obsolete final.
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W8JX
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« Reply #19 on: February 28, 2011, 07:00:25 AM »

I used a Clipperton L in heavy contesting on all bands for 15 years before selling it ( deed restrictions at new qth)  Worked flawlessly and the 572Bs lasted a reasonable 4-5 years considering ther workload. 

You will find that if you reverse the airflow on the cooling fan in the "L" (have it draw air out rather than blow it in) that amp and its internal components will run much cooler and last much longer. I did that to my Clipperton QRO 16 years ago when I re-tubed it and final are still very strong and front panel is cool to touch even after hours of usage. Not sure why "Denny" ever had fan blow heat for tubes into case rather than suck it out.
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KF7CG
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« Reply #20 on: February 28, 2011, 10:42:23 AM »

You blow air across the hot parts of tubes first when there is a possibility of condensing humidity where the amp is in use. Heating the air significantly reduces the chance of condensation on internal parts of the amp that do not generate heat.  Starting from cold in a high humidity environment one might get condensation in the HV supply or some other less than happy place.

This doesn't do much for overall cooling, but can help solve a humidity problem.

KF7CG
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W8JX
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Posts: 5364




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« Reply #21 on: February 28, 2011, 04:31:59 PM »

You blow air across the hot parts of tubes first when there is a possibility of condensing humidity where the amp is in use. Heating the air significantly reduces the chance of condensation on internal parts of the amp that do not generate heat.  Starting from cold in a high humidity environment one might get condensation in the HV supply or some other less than happy place.

This doesn't do much for overall cooling, but can help solve a humidity problem.

KF7CG

I completely disagree based on first hand observation not theory. Transfer of heat is based on temperature differential between air and device being cooled. When flow is reversed it draws cool air over tank circuit and power supply components and then over finals which are very hot and cools them and then removes heat from case. Result amp runs very cool. The way you suggest as superior take cool air blows it over hot finals and then the heated air heats up tank circuit, front panel and power supply components and heats them further than just with there own dissipation. With stock cooling amp got very warm/hot to touch and even front panel too and now it is cool and no rust/condensation issues.  Your theory is not sound in application here.
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K4PDM
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« Reply #22 on: March 01, 2011, 03:44:39 AM »

Hmm...the Clipperton-L I bought a month ago has a replacement Radio Shack fan already blowing out from the back.

The amp does get rather hot on top, however. I've thought about adding a fan blowing toward the tubes from the right side to hopefully improve the cooling.
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W8JX
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« Reply #23 on: March 01, 2011, 04:47:40 AM »

Hmm...the Clipperton-L I bought a month ago has a replacement Radio Shack fan already blowing out from the back.

The amp does get rather hot on top, however. I've thought about adding a fan blowing toward the tubes from the right side to hopefully improve the cooling.

Try this as well, remove top cover and rotate it 180 degrees and place it back on amp. You will find front and rear screw holes still line up. Then with reverse air flow and cover cool air is brought in over tank circuit and power supply caps and sucked out over finals. Also make sure that screen that is over fan is moved to inside between fan and chassis as it offers less flow restriction on suction side. 
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KF7CG
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Posts: 800




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« Reply #24 on: March 01, 2011, 11:10:42 AM »

W8JX

"I completely disagree based on first hand observation not theory. Transfer of heat is based on temperature differential between air and device being cooled. When flow is reversed it draws cool air over tank circuit and power supply components and then over finals which are very hot and cools them and then removes heat from case. Result amp runs very cool. The way you suggest as superior take cool air blows it over hot finals and then the heated air heats up tank circuit, front panel and power supply components and heats them further than just with there own dissipation. With stock cooling amp got very warm/hot to touch and even front panel too and now it is cool and no rust/condensation issues.  Your theory is not sound in application here.  "

You missed my point entirely! It had nothing to do with the efficiency of cooling and everything to do with the prevention of moisture collecting where it shouldn't be. Condensing humidity can and does cause arc overs in areas that have consistantly high humidity. The equation at startup is: Moist air, cold components, wet circuits, and then Bang! I haven't seen it happen with an amplifier but have seen it in the high voltage charging circuits of some Van de Graf generators.

It may well have been that the airflow direction was a bad choice on the Clipperton, that is for field tests to determine. But in an unairconditioned radio shack in the jungle it might not be so bad.

KF7CG
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W8JX
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Posts: 5364




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« Reply #25 on: March 01, 2011, 05:45:00 PM »

"Maybe" if you are in a rain forest you blowing hot air in "might" work for moisture but that is questionable. You will get no condensation with negative pressure air flow unless you are in 100% humidity and if you are you have bigger problems. Their is nothing gained by running internals much hotter and shortening their service life on a the dream whim that it will rust otherwise.
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