[HBR] 6BE6 Mixer Question

Thu Mar 3 16:11:40 EST 2011

Many fine receivers from the "pre-SSB era" exhibit a frequency shift under AGC/AVC action. (The HQ-180 because it has a true product detector actually fares better in SSB than many other receivers.)

Hammarlund dropped the ball a little bit because in most of their receivers in this era, the 6BE6 is under AGC action. The SP-600 will do the same. Drake as you point out was more cognizant of the gotchas. Instead of using pentagrid mixers, Heath often used TV-type triode-pentode mixers (especially 6EA8) in many of their 60's rigs to good advantage as mixers.

Some swear up and down that the 6BY6 will be better than the 6BE6. Others swear the other way :-).

My solution was always to turn off the AGC if the warble bothered me. Although it was sometimes irritating that the RF gain knob worked as RIT even then. In fact, a lot of things about AGC bother me. Loud signals should be loud and weak signals should be quiet. Just my two cents :-). At least the HQ-180 made the right choice of having a true product detector.

-----Original Message-----
From: hbr-bounces at mailman.qth.net [mailto:hbr-bounces at mailman.qth.net] On Behalf Of Byron Tatum
Sent: Thursday, March 03, 2011 3:24 PM
To: HBR at mailman.qth.net
Subject: [HBR] 6BE6 Mixer Question

Hello-
    I apologize for being a little off topic for this list, but I posted this 
question on the Hammarlund list and it does not appear to be real active at this 
time. I know there are a lot of real knowledgable folks here.
    My question is in regards to the application of AVC to the signal grid of a 
6BE6 converter tube. I know there are receivers that function fine employing 
this, but I believe I have a problem in my HQ-180. There are two signs of a 
problem - one is when listening to SSB when the RF Gain knob is changed there is 
a shift in frequency, the other is with strong AVC action there is a slight 
warbling.
    I saw on one fellows site regarding the HQ-180 where he mentions this 
problem, and disconnected the AVC from the 6BE6 converter (455 KC converting 
down to 60 KC). I have studied doing this, would it be as simple as just 
disconnecting the AVC from the signal grid? In the circuit for this particular 
converter, if the AVC is disconnected from the signal grid (Pin #7) there is no 
DC ground for it. I would imagine that I would need to provide a DC ground path, 
via a resistor or possibly RF Choke? I looked at the 6BE6 converter circuit in a 
Drake 2B and there is a DC path to chassis through the RF transformer feeding 
the signal grid, with no AVC applied to it.
    While speaking of the HQ-180 does anyone have any additional information 
regarding improvements, updates, etc? I performed the Dallas Lankford AVC 
modification in mine and it was very much worth the trouble, it was simple in 
that one resistor was bridged and a capacitor added. I read where Dallas 
published a compendum of HQ-180 manual additions but he has become hard to 
contact now and does not give out his email adr. My HQ-180 has the verier tuning 
update (from factory) and I noticed a website where this update instruction set 
was provided.
    I have always wanted a nice HQ-180, when I tested for my novice license in 
the late 1960's the Ham here in my hometown that I had introduced myself to had 
the HQ-180 / HX-50 combo. I had never saw any of this gear in person, but had 
all of the Hammarlund brochures. I thought the HQ-180 had to be the ultimate 
receiver back then. The OM, however, was frustrated with all of the hassles, etc 
and one day I went over to visit and all of the Hammarlund stuff was gone and a 
Drake TR-3 was there, and he was much more content. But, I enjoy tinkering with 
this old receiver, and have upgraded it to the separate filament transformer for 
HF Osc. and first mixer as done in HQ-180A. I removed the 5U4 rectifier and 
mounted a nice mil-spec 8H. choke in its spot and went to solid state diodes, I 
can tell the difference in the heat of power transformer. I replaced the filter 
capacitor with one of much greater value in the 3 sections for B+. I wanted to 
lower the B+ some, and have mine around 225 volts now downstream of both chokes. 
After I finish burning in the set for a good while I plan to go through an 
alignment, the RF portion looks reasonably close as of now but I believe the BFO 
is not quite spot-on with IF.
    Enough of my rambling, if anyone has any info on this receiver I sure would 
like to hear from you.
                                                    Thanks, Byron WA5THJ   
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