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 Post subject: 6146's in an SR-150 xcvr
PostPosted: Feb Sat 03, 2018 2:02 am 
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Joined: Sep Thu 20, 2012 3:42 pm
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Location: Salem, OR
Just pondering the idea of putting 6146's in place of the 12dq6's in an SR150 Hallicrafters transceiver. Are there any advantages? Doesn't look too difficult. Anyone out there with any knowledge of such a mod? May be a total waste of time, but was just wondering.

Marc-k7wxk


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sat 03, 2018 6:43 am 
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Location: Lincoln City, OR
Greetings to Marc and the Forum:

I would measure the dimensions of the PA cage and the distance between the sockets carefully. 6146's might not fit. I don't know what the advantages would be....
I think 12DQ6's are still readily available.... and so are 6DQ6's if you want to modify the heater wiring slightly.

I haven't priced 6146's lately, so there might be some economic advantages... be careful of neutralization.... 6146's have significantly different inter-electrode capacitance values.

IMHO, not worth the trouble.

Regards,

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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sat 03, 2018 3:31 pm 
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I agree with Jim that it isn't worth the trouble and usually operating conditions are going to be different between a typical low power transmitting tube like a 6146 or 807 and tubes intended for TV sweep service which were designed to develop very high current at fairly low voltage in a form of pulse service. Often you will find that drive requirements are higher and power output is lower after you switch and as Jim pointed out the neutralization circuit may also require changes.

I wouldn't do this to a SR-150 either unless it is basically in near junk status. Its final tubes are rare or expensive and the 6146 tubes aren't going to provide an advantage over the stock finals in terms of operating performance. As long as the "sweep" tubes are treated reasonably they will have a long service life in this transmitter.

For a short time it was very popular to change the finals in the very popular FT-101 to 6164 types and with modification this works but not like or as well as it does with its original sweep tubes. I prefer transmitters with "real" transmitting tubes but if the unit was originally designed for sweep tubes then it is going to work best with them and proper utilization of a different type of tube will at least require significant changes in the final circuit and quite possibly earlier in the exciter chain and maybe in the power supply. Sweep tubes, in general, will perform better (in terms of power developed and efficiency) at lower voltages than comparable transmitting focused tubes because the tube engineer designed the tube for its intended type of service. The interesting but little used 7094 was sort of a cross between a sweep tube and a high power transmitting tube because it was designed to stand up to transmitting service but also provided the typical sweep tube characteristic of high current flow at relatively low plate voltage.

Rodger WQ9E


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sat 03, 2018 3:51 pm 
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Location: SW WA state
As usual Rodger, you are a veritable fountain of information! Now I will have to look up the 7094....

-Tom

rsingl wrote:
The interesting but little used 7094 was sort of a cross between a sweep tube and a high power transmitting tube because it was designed to stand up to transmitting service but also provided the typical sweep tube characteristic of high current flow at relatively low plate voltage.

Rodger WQ9E


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sat 03, 2018 4:34 pm 
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Joined: Sep Thu 20, 2012 3:42 pm
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Location: Salem, OR
Thanks Gents,

I guess I'm not surprised by your answers and recommendations. This is what happens when one gets bored and starts to think up stuff. I don't have an SR-150 yet, but am considering adding one to the collection of classic rigs in the shack. This was the first modern transceiver I had ever seen when I became a ham back in '65. Of course, it was only a pipe dream back then. I think it is a rig that I could successfully resurrect with a little effort. Any pitfalls out there to avoid would be greatly appreciated.

Thanks again,
Marc-k7wxk


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sat 03, 2018 9:25 pm 
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Joined: Aug Fri 01, 2014 11:18 pm
Posts: 31
Hi,

I have a Hallicrafters SR-160 tri-band transceiver where a previous owner had changed the finals to 6146s. In addition to rewiring the sockets, the screen voltage was regulated by a zener diode (nice touch) and the neutralizing circuit modified to account for the differing tube characteristics. I think the 6146s would have been happier with a higher B+ voltage than what is provided by the standard SR-150/SR-160 PS-150 power supply (think maybe 700v rather than the provided 575v). In addition, the VFO had been replaced with a solid state VFO that is nice and stable, but makes the rig totally non-original and short of replacing the VFO circuitry with parts from a donor, there is no way to return the rig to original condition. Given this, I decided to modify into an SR-500 by changing the finals (again) to 8236s along with some other relatively minor changes and using the PS-500 power supply. However, I probably wouldn't have done this if it weren't for the irreversible changes made before I got the rig.

Also, I posted a while back that when I replaced the 12DQ6s in my SR-150, it would no longer neutralize properly. I went through my entire collection of SR-150s and 12DQ6s and concluded that 12DQ6s made in Japan would not neutralize correctly given the factory stock neutralizing capacitor. I did find an alternate capacitor having a greater capacitance range that allowed proper neutralization, but this just illustrates that even replacing tubes with the same type, but different manufactures can lead to unexpected results. As a classic example of unexpected results, just look at the plethora of posts on various forums regarding the 6146, 6146a, and 6146b tubes. Lots of erroneous information out there, but it just illustrates how sometimes what seems like a simple thing can lead to unexpected problems.

Bob, AB1MN


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sat 03, 2018 9:57 pm 
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Interesting Bob, I think I put RCA finals in my SR-150. I know that Drake preferred Sylvania finals for the 4 line and that is what it would get for factory service but I have used several different brands in my 4 lines without issue. One tube definitely to avoid is "Servicemaster International"; some of them may be OK but in my experience some of the Chinese exporters would even be embarrassed to sell them.

Marc,
I can't think of any special issues with the SR-150. I don't care for the inconvenient lack of a plate current meter but you can monitor across the provided resistor and terminals in the matching power supply. Be aware that the meter leads will be at full plate voltage above ground when using this measurement provision so use caution, especially if you permanently add a meter.

Also check that the switch on the back is set properly for the common/separate receive antenna setup and a lack of receive sensitivity, when set to common, occurs when these switch contacts get dirty so exercise it a few times.

Rodger WQ9E


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sat 03, 2018 10:18 pm 
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Joined: Sep Thu 20, 2012 3:42 pm
Posts: 381
Location: Salem, OR
Great info all. I prefer stock when dealing with the classics, too. The only reason I thought about the 6146's is because I have a Heathkit HP-23a that could be modified to power the SR-150, but it has a lot higher B+. Didn't know if the 12dq6's could handle upwards of 750v that is supplied from the HP-23a. If I pursue the SR-150 I will probably do it right and get the matching power supply, but man the sellers are proud of them.

Cheers,
Marc


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sat 03, 2018 10:46 pm 
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Marc,

You may be able to use the HP-23 supply OK. The higher voltage won't be a problem for the final tubes since it was subject to very high positive pulses in its intended application as a horizontal output tube. You will have to adjust the bias setting to come up with a tube resting current that stays within reasonable dissipation ratings while also staying in the linear portion of the operating curve.

Use the low B+ selection for the HP-23 which is close to the 250 volts supplied by the PS-150.

The Hallicrafters supplies are less common so the price is high. A Drake AC-3 or AC-4 might be a good compromise since its HV output is a bit lower and although somewhat expensive they are much more common than the Hallicrafters supply.

And on edit: If you decide to roll your own power supply the transformer out of a Yaesu FT-101 series should make a good starting point. These show up often in parted out transceivers and apparently it is a good unit because the CBers rarely managed to burn up the transformer while frying every other high power component in the rig.

Rodger WQ9E


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sun 04, 2018 12:11 am 
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Location: Costa Mesa, California
Marc,

I have two SR 160's and the HT 44. I have two of the PS-150-120 power supplies. The power supplies came with the purchase of the radios when I bought them. I would suggest you look for a package deal if you can. It will cost much less than trying to acquire each individually. In fact, I bought one of the SR 160's just because it came with the supply.

The HV from my PS-150-120 runs at 650 VDC (manual shows 575) and of course the power cord has the Drake style connector, so as Rodger has suggested, the Drake supply would offer an alternative--and it has the connector already attached. The wiring to the connector is NOT the same. Both supplies have a 250 VDC LV, and 12.6 Filament voltage, with the Drakes filament current rated more than sufficient.

Norm

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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sun 04, 2018 2:32 am 
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Joined: Sep Thu 20, 2012 3:42 pm
Posts: 381
Location: Salem, OR
Again Gents,

Thanks for all the good poop. I like the idea of a package deal. They come along every so often, and it's not like I NEED another boat anchor. Thanks for the reassurance with respect to the higher voltage on the HP23A. I suspected that the 12DQ6's could handle it, but wasn't sure. Now to find a deal I can't pass up.

Marc-k7wxk


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Sun 04, 2018 7:30 pm 
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Joined: Feb Sun 10, 2013 3:31 am
Posts: 50
Hi Marc,

The tube vendor that I use has the 12DQ6B for $9.20. That is for New/NOS tubes. They also sell several used tubes, tested. Not this particular one, though. I sometimes buy used when I'm doing the initial testing on a restoration. I'll add the 2 Hallicrafters rigs to my hamfest watch list. A friend of mine a long time ago had the SR-150. I have a Tempo AC one power supply that runs 600 VDC for the plate, might work for the Hallicrafters rigs.

The URL is http://pacifictv.ca/

Good luck,

Ted, KX4OM


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 Post subject: Re: 6146's in an SR-150 xcvr
PostPosted: Feb Mon 05, 2018 6:17 am 
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Location: Costa Mesa, California
One of my SR-160's came with 6DQ5's in place of the 12DQ6's. The 6DQ5 was used in the HT-44 and has a little more power than the 12DQ6's. It is an easy swap, with the wiring changed so that the heaters are in series instead of parallel, and the pins re-wired to reflect the other differences in the tube layout. Yesterday I put that SR-160 on the bench and re-wired it for 12DQ6's and finished changing the paper and electrolytic caps. One big problem with the 6DQ5's is they are a taller tube and the lid for the PA compartment won't fit--only 1/8" clearance to the HV plate cap. I had to make a new lid because the radio came with none. The plate caps are different sizes for the two tubes and I fashioned new plate caps for the 12DQ6's from some large Fahrenheit clips. The radio works well and I am doing the alignment now. The PA needs neutralizing, but after that, there doesn't seem to be any problem that an alignment won't resolve. This radio has other issues--mainly an assortment of knobs that are not original, but the case and panel are very nice.

Norm

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