Topic: Finished Project: Building My Monaural Playback System

[mfrench]

OK,.... I've wanted a mono playback system for quite a few years. I've tried a couple of times, and met with limited success. I actually have quite an extensive amount of mono and 78's, so this will be a worthy effort.
Towards this effort, I scored a 1957 Harman-Kardon Prelude PC200 10watt integrated mono tube amp on CL. It's in great shape and works perfectly.
I also have a 1953 Presto Recording Corporation 15G2 turntable, and a 1955 GE A1-500 transcription broadcast tonearm, with an NOS GE VRII TriplePlay cartridge from the mid-50's. This is the cartridge that has the red handle on top that you use to turn the needle from LP to 78.
So, I've been accumulating parts for a mono system for a while now, and have all the components. I was just stuck on what to use for a cabinet.

[mfrench]

What's in the Truck?




Old phonograph and radio cabinet from an era when 78 ruled, and amplification was just being introduced. It seems to be of British descent.

The arm is extremely heavy, labeled as, Harlie. It has a steel phongraph needle from the "victrola/edison" era, that is also an electronic pickup that feeds to an old tube amp.
The turntable is hand cranked. Its very noisy in its bearing and runs at about 68->70rpm
I have no intention of using it with this arm, TT, or the amp. I'm purely after it for the cabinet and will be replacing components with more modern gear.

Hand cranked TT:




Platter, from when they even made the unseen details pretty:

label:

platter off for the first time in??


rear of cabinet and guts:


old integrated amp (radio, and, phono):


spare tubes - Osram (also labeled as British General Electric) and BVA:




Rola speaker:


Motor:

[mfrench]

My intention is to gut out the old original stuff, which is really not working - the TT spins, but slowly, and not very long. The amp is dead, and would take a major overhauling effort (that I know nothing of).

I got to tear this thing down this afternoon. I got the amp out, and the speaker out.
The speaker came to life when I touched it to a 1.5v battery. So, I dug in deeper and pulled it out.
Its a nice paper cone, rippled edge. It had a transformer attached to it. When I hooked it up to the HK 10w, I had to turn it it 11 to hear anything. So I took the transformer off, total change, and the thing started making really nice sounds, but sounded stiff, as it had sat for 15 years unplayed by the sellers suggestion.
Its been playing for a couple of hours as a mini open baffle leaning against my stereo rack, and it sounds really nice - its a keeper.  There is a slight tear in one area, but I was able to massage things back together fairly well, and its inaudible.
Suggestions for gluing this together?
The tear is directly behind one of the frame supports making it a bit difficult to access. I think a rear repair would be better, and I can reach it with some effort. Overall its a really nice sounding speaker.
There is no dust cap.

[mfrench]

When I took the speaker out today, it allowed me to remove the old stained speaker fabric. I replaced it with a reed place mat / grass cloth. It didn't effect the quality of playback and looks WAY better than that urine stained(?) fabric. There was quite a bit of cat hair inside the cabinet,  and kibble snacks of some kind.

So, I used the old original speaker wire, and soldered it back to the speaker leads, along with some heat wrap to keep things tight.
So the speaker is wired with old vintage cloth wrapped wire; steel wire?
The cabinet is a resonant design. Half of the floor of the interior, immediately below the speaker, is open to the floor, and the rear is also open and fires into the corner.
The thing has some fairly massive bass response with the little speaker!

at any rate,.....
we ordered a new couch last week - so, forgive the ugly old leather thing - its 12+ years old and is my sweet spot for the stereo system listening, and well worn. We're also readying for a paint job amidst all of this.
This mono system sort of fires back towards my stereo rack. And being a mono corner speaker it fills the whole room w/ music, in a nice blending without so much of a source influence - its just a room with music in it.

This is essentially what I have in my mind, but far from being finished (below pics). I just need to find a new facade material for surrounding the amp, and making it blend in naturally. I'm thinking perforated copper screen, or perhaps something like acrylic tortiseshell if I can find it;  and cut it to a tightly scribed finish around the H-K amp.
For now, its making wonderful mono music in the corner, and sounding damn vintage and appropriate.
And,... Sarge has totally changed her tune - SHE LOVES IT!!
After todays tear down and gutting session,....



Note:
Since the pics, I've moved the TT to the cabinet top to test for acoustic anomalies, feedback hum etc., and it passing the test thus far.

[mfrench]

the vintage components:
This is the deck that i'm going to use; a Presto Recording Corp. 15G2, from 1953. Its a three speed idler drive that I've been restoring, and have working perfectly now, complete with a newly retread idler wheel.


This is the GE A1-500 arm for it, from 1955, possibly earlier (it was on my 1955 Presto T18 turntable):


Harman-Kardon Prelude integrated 10w mono tube amp, c. 1957

[mike1061]

So you weren't happy with the sound of the other TT, with the mono arm added?
Thanks Mike

[mfrench]

Which arm, Mike, the original arm?
If so, it weighs about a pound at the needle, tracking force, and will cut records to ribbons. Some of the old shellacs had a series of check boxes on the labels, for around 50 plays, before they were dead, due to those hayfork tine needles.
The more modern arm that I'm going to mount will allow for 4 grams of tracking, compared to the literal 16oz of tracking force from the other arm. The 4 gram GE VRII will not damage the records.
And I want to play 33 mono. The original table only spun at 78 (actually clocked at 68 at full windup), and its bearing / gearing system is really, really noisy.
So, a new deck will add versatility with the other two speeds.
I've been spinning Chet Atkins, Johhny Cash, Buck Owens, Doris Day, Kay Starr, Guy Lombardo, and a bunch of Big Band stuff at 33, and it sounds so nice presented in a vintage format.

[it-goes-to-eleven]

That is gorgeous!

I have an old one I've been saving (I think it is an rca). Or, rather, am keeping at my folks'.  It has a turntable and shortwave.   For now, it is just being used as an end table.  I understand demand isn't that great for them, so they aren't worth much.   I hate to gut it..   The shortwave works, so I'd like to keep that.    Some day..

[mfrench]

I hear you on not wanting to damage the original parts. i was looking for a gutted project cabinet so that I didn't have to do that; but this thing sang its siren song to me,....
The amp is so far gone and toasted that it would be a complete overhaul from scratch. Tons of wires with insulation that has fallen off. The amp and TT were so far gone that I don't feel so bad about gutting it. The TT might be a worthy package for someone who wants an early amplified TT, as it spins up, and might just need a refreshing. Bu at present,.... really noisy.

What I'm going to do in this is replicate the originals, with modern parts that will look correct, and fit the exact dimensions of the originals, so that it can be reassembled to original. I don;t sell my builds, so I doubt its going anywhere for a while.

I have a friend who is a vintage tube guy, and up til recently, has worked in the radio broadcast biz as a trouble shooter, engineer.. He's an electrical engn'r by training, and knows tubes like the back of his hand.
I might have him take a look at it, and see if it can be restored. Its a complex bit of wiring below the hood though, and would be a massive dig to get anything done. I know nothing of tubes, so I'm out.

[Gutbucket]

Sweet cabinet. I'm intrigued by the part-mechanical / part-electric nature of the original player. Cool iron platter casting.  So it was a wind-up mechanically driven platter, with electric amplification and the output transformer mounted directy on the speaker.  Is there some sort of coil mechnism cartidge inside the head of the TT arm which the steel needle fits into?

I was just thinking of you a couple weeks back when I was up in NC at a country blackberry festival in an old CCC era stone school with some old-time music performers playing and a junk sale with loads of old 78's.  I was tempted to bring a load home, but realized I'd probably never get around to doing something with them.

What does the contol labled contour on the Harmon Kardon do?

[mfrench]

Hi Lee,
I'm still learning about it, and had to refer to the manual.
There are several different ways of "shaping" the sound with the amplifier; Rumble Filter, Contour, RollOff, phono-input EQ selectors (3x), and the Bass/Treble EQ setting knobs. I've played with all of them, but unsure as of yet, how to describe the functions.
This is a copy of a manual scan pdf, of the contour information:

[Gutbucket]

That's serious tone control.

Seems to have high/low-pass filters, high/low-shelving eq, 'loudness curve' eq, and the 3 phono-input eq's.  I know there were a number of different playback eq curves used in the early electrical recording era- as I understand it each record manufacturer/label used their own curve for years until the eventual RIAA standard.  I'd guess the phono-inut eq's let you switch between 3 of those.  I'm sure you know far more of the details about that than I, though. If there was any question before, there is now no doubt that you are Mr. Record Guy.

[Jimna]

pretty cool, moke.  my mom really digs antiques too.  It was funny as I started reading this because Im pretty sure she has 2 of those (or close facsimile) in her house now....not because she is into vinyl, but because she thinks they look appropriate near modern media(ie TV ) to off set them in the room...she really likes old shit.     

If your going to modernize it this much why not make it sound better too?....yes I realize a mono source is still mono but why not polish that turd a little?

[mfrench]

I felt, for the longest time, especially after spending so many years trying to understand stereo recording; i felt/wondered what the heck do these folks see in this older mono stuff?
About a year and a half ago, i started hanging at an old record player restorers site. There were some guys there that were putting some serious time and serious bling into mono systems.
I've listened to mono now for a year and a half, in stereo.  The signal was mono, but it was processed by stereo gear and going out to a stereo pair.
While it sounded fine, it was an odd, not really right sound, but hard to describe the not-rightness.

A couple of weeks ago, I found that HK amp for a steal on CL. So I bought it.  I ran it into a single David Bogen Corp full range mono 12" speaker. The speaker I used came from one of those old suitcase record players that they used to use in schools and used in square dancing.
At any rate, the spkr came in its own open baffle-type cabinet, so I pushed it into a corner. Traditional mono speakers were frequently placed into corners to increase bass response, and broadcast into the room in a diffuse seeding of music. The sound that speaker made from the corner was really cool. It completely filled the room up with sound, and was fairly indistinguishable as to where it was coming from; but the whole room was alive in music, and sounded nice regardless of where you were. The stereo does this too, obviously, but, is best enjoyed in one 2sq.ft square spot in the room - beyond that sweet spot and it might as well be mono.
As far as frequency spectrum goes in playback with the cabinet speaker,....
it will carry a cello very well. It gets a bit bloated in the string bass notes, but thats a cabinet issue that I'm going to address with some cabinet tuning to increase projection a bit, and reduce the bass blossoming of a resonant cabinet design. Resonant cabinets are making a significant comeback in stereo playback these days, as people are moving away from high wattage amps, and going for micro-wattage, literally .75w amps. They like the old style cabinets because they are only using a single driver spkr, without any crossovers, and allows for insane sensitivity for those micro-wattage amps..
The cabinet increases the bass response, naturally, and gives a nice fat tone.
This old cabinet is an original resonant cabinet design that todays cutting edge speaker manufacturers are touting as modern. It really does make some nice sound. But I know I can shape it a bit with some internal bracing that would cause the side walls to flex a little less, reducing bloat. There are also two "ports" that can allow me to tune the amount of sound coming out the rear of the cabinet, and one that redirects it towards the floor. In this effort, I found that when I placed a piece of 1" neoprene foam kneeling pad within the spkr cabinet, and leaned it diagonally behind the speaker, I was able to sharply reduce the corner bass response and make it more articulate by directing it down and out the bottom of the cabinet (both the rear and floor are "ported"). So I'm going to create a tunable internal diagonal baffle that can be set to different angles to change the amount of rearward projection.
I'd love to have something like an old Quad ESL speaker (looks like the rear seat of a 47 packard), or some Klipsch corner horns, Altec Lansings, but it takes more room than I have - they're truly massive spkrs. When we get the larger house (and Sarge is looking), I'll have my dedicated listening area, and will have a glorious large scale mono system - but they are not small, make no mistake. For now, this small console fits our house and Sarge loves it.

[mfrench]

Sweet cabinet. I'm intrigued by the part-mechanical / part-electric nature of the original player. Cool iron platter casting.  So it was a wind-up mechanically driven platter, with electric amplification and the output transformer mounted directy on the speaker.  Is there some sort of coil mechnism cartidge inside the head of the TT arm which the steel needle fits into?

The pickup head is traditional in its size and weight. Its really heavy.
The arm is bakelite, and hollow out to the head. The head has some sort of processor in it that takes the needle motion and converts it to electrical signal.
I have not hooked it up, but, I did put a DMM on it, and found that I can create a DC voltage load by tweaking the needle sharply. So it seems to still work.
It is wired to a 1/4" audio plug. That audio plug went directly to the integrated tube amp, in a traditional connection. The radio is also built directly onto the amp, literally an early integrated amp.
Just last night I found that the pickup head rotates around about 90º, assuming to get the needle to clear the record, or for needle changing. It also seems to disconnect the pickup, for what I assume to be feedback resistance in radio listening.
This is one of the earliest examples of an electronic pickup and electronic amplified audio systems. Its components are just totally dead, and I don't have the interest, nor funding, to throw at restoring the old amp - I can see that easily going over a grand.
As I do with all of my renovations, its all being done so that it can be brought back to original. I will box and save the old amp and TT, just in case I hit the lotto and can afford to OH it.

edit; to finish my thought,.....
You'd asked about the transformer as part of your thought.
The transformer is there, for what I assume to have been an attenuator for the speaker. When I first hooked it up to the amp, I had to go to 11 on the suck knob to hear anything at all.
When I removed the transformer, the speaker jumped to life. It had been silent for 15 or 20 years that this seller had owned it. So it sounded really stiff at first. Since then its loosened up considerably, mellowed, and is a really nice sounding speaker.
So, I'm guessing that the amp was too much for the speaker and it had to be attenuated via the transformer.
The speaker is really sensitive. I can tell that 10w is giving it plenty of a workout. Its a nice match of plenty of power to drive it, and nice detail at low levels.

Paper speakers are said to take a good 25 years to loosen up entirely. So if the voice coil is still loose, they'll last forever, if not abused. There is no foam surround, just paper.
A couple of mono enthusiasts have suggested that I give the cones a treatment of Franklins Tightbond II wood glue. Its said to be a major improvement in the woofiness of the bass.
There is a slight non-distorting tear in the speaker. They said to get a cigarette paper, and tack it to the speaker and then glue-paint the cone, and leave the surround uncoated.
I'll take these guys advice, as they actually grew up with the old vintage gear and have an encyclopedic mental database on the stuff.