Hilton HP-95 Square Dance sound system project

[sluckey]

...found -26VDC on pin 3.   Interesting.  Not something you see very often.

Really? I've never seen that.   

[ShoemanGB]

 Um,  not sure what to make of that Sluckey     Am I completely off base with that reading of the circuit?  Would not be the first time and sure won't be the last.   I see some hi-fi designs doing that, and this was a record player amp by design.
 I assembled it back in the case which let me have the internal monitor speaker (6X9) in play.  So it turns out that plugging into the now modified turntable input gives you the options of silencing the PP output stage and using the monitor level control on the speaker grille to run the SE output by itself,  or you can dial the SE to silent and run the PP by itself.  The music only/voice&music switch lets the mic inputs through the Se end but you can't silence the PP output on V&M mode.   Maybe a master volume is in order.
Anyways,  that was a great discovery.  Lots of flexibility built in already.    Re-flowed a bunch of joints too trying to make it as quiet and glitch free as possible.  Got to order some more resistors too. 
Thanks to everybody that has weighed in with advice so far, it is appreciated!

[sluckey]

Um,  not sure what to make of that Sluckey     Am I completely off base with that reading of the circuit?

Haha. Not really. But I bet that -26v ain't on pin 3. 

[PRR]

Fix-biasing an SE amp costs more and is less safe. It may gain a part-Watt but if you are that hungry get two half-size tubes in push-pull.

In THIS amp, they have the main channel already fix-bias push-pull for maximum swing in minimum travel weight. So a fixed-bias SE monitor amp is not stupid.

But yeah: not pin 3.

[ShoemanGB]

Alex Trebec " I'm afraid the answer the judges were looking for is pin 5, pin 5. Sorry. And how much did you wager?"

My bad.  Blame it on my wife asking me a question as I headed to my laptop from the bench repeating to my self minus 25 on pin 5, thus blowing my memory trick all to pieces.  PRR's observation makes sense, the money was already spent and parts were in place.  I think I'll convert it to cathode bias and see if I can hear any difference. Makes sense to do so just from a reliability standpoint.

[MartyAbts]

I have an HP-95, but it is an earlier one (SN 150033 vs 150879).  Instead of the 6C10, mine has a 6AU6.  The former is a three triode tube; the latter is a single pentode, so the circuit must be a little different in order to achieve the same functionality.

My "sound system" came with two speakers: JBL Signature Speaker - Model D123, 16ohm, made in the late 50's.

[ShoemanGB]

Guess what found their way home this week?  Yep, the previous owner brought me both the missing speakers. Cool stuff.  I puled the grille of one to get a look-see inside.  JBL D123's, and it's a folded horn sort of design with an internal baffle that is slotted in the back feeding the outer section, or shell I guess, that has outlets on both sides of the cab.  That explains why the wire mesh wraps halfway back the cab sides...it's not solid there. 
 I plugged it in the my amp and it makes very nice clean tones. Can't try it cranked as the misses has a bad case of bronchitis and needs her rest.... we have a Phish show to attend next Saturday. 
 I'll try them with my stereo too as that's the designs intent. Might make a decent set of industrial looking floor speakers. Way to big for a bookshelf. But they do have holes underneath for pole stands.

[cspar]

Wow that's a pretty cool unit and the speakers are icing on the cake.

Is the turntable platter full sized? It looks like it is from the picture when compared to other Hilton models.

Nice score.

[PRR]

> Is the turntable platter full sized?

Scaling off the center-post to the platter edge on the image, I figure 11.4 inch. Enuff overhang to get fingers under.

[cspar]

Yeah, looks like nice platter. Especially for an old portable unit.

There's one on ebay currently that doesn't show the model #. Although he didn't mention his platter it looks that it might be the simpler version like MartyAbts has since it has a smaller platter?

The ebay listing shows a picture of a label on the back that says the monitor circuit is patented with other patents pending.

I looked around a little for the patent hoping for an intresting and informative read but had no luck with my searching.

Although obviously different in purpose and design the monitor circuit reminds me of both the cab emulator part of Nachbaur's Dogzilla amp and Cook's FuzzniKator preamp.

I've had that type thing on my mind though since I've been brainstorming and working out different ways to do a germanium radio/reel to reel conversion hybrid lately.

I'm up to 6 reel to reel players in various stages of conversion and concepts. Some playable, some still stripped, nothing quite finished but things learned and progress made.

Enough of sidetracking with my single ended salvage summer study though.

So in returning to the topic, if anyone happens to come across the patent for the monitor circuit and posts a link, I will be one of the thankful people that reads it.

Really interesting and cool unit you've got there. Too bad they're so rare.