[SixClub] 6m Converted SB-220 Amp for Sale

[Roger (K8RI)]

On 5/22/2010 5:24 PM, kd4e wrote:
> As our youngest used to say when he was 3, "Naaauuughty!"
>    
You do realize you can purchase tested and guaranteed YC-156 pulls for 
about the same price as a pair of 3-500Z's? They produce a signal with 
very low 3rd order IM.  40 watts of drive with 3KV on the plate will 
give the legal limit out. Running at those ratings THAT tube would 
probably still be working for your great, great, great grand kids...if 
it didn't get gassy first. <:-)) Also the YC-156 does not require a 
socket. The grid flange bolts directly to the chassis with filament 
leads/cathode bolting directly to the tube rings.

Unfortunately there is one problem with the YC-156. Its size!  It's 9" 
tall and might require a tad reworking of the 220's cabinet. <LOL> That 
and maybe a heavier chassis as the tube weighs 9#. OTOH with it's size, 
at that power setting you could most likely cool it with the muffin fan 
out of the 220.

I happen to like Tetrodes. My current amp uses a 4CX1500B, or the 
Chinese equivalent, the FU728F. I should point out the two use different 
filament voltages though.  The 4CX1500B's are readily available at a 
fraction of the 8877 price while the Chinese version is available new 
for about a third to a quarter the cost of a new 8877. BTW IM products 
are in the minus 50 some db range while most ham amps run in the low to 
mid minus 30 db range.  My favorite is the 4CX3000A7.  It too is 
available at  reasonable prices, is a bit shorter (but not much) than 
the YC-156 and only weighs about half as much. It requires testing for 
low IM in production and a guaranteed output level. UNFORTUNATELY it 
uses a socket like the 4CX1500B's on steroids which costs more than the 
tube when we are talking pulls.    The big advantage is it's almost 
instant on without the warm up time associated with 8877's, and 
4CX1500B's.  That does come at a price though.  The filament takes 9V @ 
45.5 amps. IOW 375 Watts!<:-)) Of course that's great in a chilly shop 
during the winter months. That and you can set your coffee cup over the 
air outlet on the amp to keep the coffee hot. Spill protection might be 
advised though.

BTW these tubes all work great on six while the 4CX3000A7 also works on 
2-meters at full output so it should run the legal limit even from a 
tired tube.

I mention these monsters as they all work well at the legal limit, are 
readily available at reasonable prices, and are unlikely to disappear 
like the 4CX1600B,
PL-172, 8873, and 8875 did. Although still in production the 8874 is 
getting very expensive for such a small tube and owners of those amps 
are converting to 3CX800s and 3CPX800s. Getting the filament voltage is 
the difficult part as there is very little spare room in there. The 
other option is to purchase a new plate transformer that has the 
filament winding for the 3CX/3CPX800A7's

Being somewhat cheap...er ... frugal I like the idea of having access to 
relatively inexpensive tubes that let me run the legal limit. Also the 
number of tubes available to the amateur market is getting smaller. OTOH 
at my age there will likely be plenty of types around far longer than I 
will be. One thing I liked about the GU84B/4CX2500 was the size of the 
tube. It made them practical for desk top amps but those are running 
around $500 USD each (give or take a bit) and sockets are running as 
high as $180 or $190 each.

I should mention that both 8877 and 3CPX800 pulls are also available for 
reasonable prices at times.

I have to wonder about the US amplifier industry and tubes as well as 
the foreign supply of tubes.  Mainly China and RUSSIA.
Several US built amps use what are apparently discontinued tubes, but 
there is a huge supply of of them as NOS so they can purchase in bulk 
and test them.
This makes me question the quality of those amps.
Some foreign manufacturers have moved from RUSSIAN to Chinese tubes due 
to availability. At least some of the Chinese tubes have some of the 
best IM figures out there.

US made tubes have become extremely expensive. I used to purchase 8877s 
for $305 in lots of one! Now they are well over a thousand dollars and I 
see some places asking close to two thousand. Even the venerable 3-500's 
bring a premium price if made in the US. However I recently talked with 
a broadcast engineer who told me they no longer get the life out of 
tubes like they used to.  Now they pull them every six months instead of 
every year or two years. His comment was, "they just don't make 'em like 
they used to". I've used some Chinese tubes (mainly the 3-500Z and 
FU728F) and so far have no complaints. I was able to purchase the FU728F 
complete with socket and chimney for about what I've been paying for 
4CX1500B and 8877 pulls.

Thing is, US tubes are high priced (out of reach for most hams) so we 
purchase from off shore.  That drops the demand which in turn makes the 
cost of manufacturing individual tubes higher so they cost more. That in 
turn sends more off shore reducing the demand further and pushing prices 
higher in an ever increasing spiral until it is no longer economically 
viable to produce them here.

73

Roger (K8RI)

>    
>> I'm having a ball with it too. Nice to be able to pop up
>> 1300+ watts on SSB What? It's a QRP rig?<:-))
>> 73  Roger (K8RI)
>>      
>