A few miscellaneous questions.

[nyjb]

Hello,

I've been working on some Seeburg Rs.  I have a few questions.

1.) I've read both Ron and Rob describe the additional fusing of the receivers, electrical selectors and mechs.  I assume you use simple inline holders, but if there's a better way...

2.) I've found the adjusting of the Electrical Selectors' lock pawls to be maddening, as even the tiniest change to solve one problem creates another.  The manual presents the vertical adjustment first, but since any adjustment of one requires a check of the other, it's more like a circle.  Does anyone have a "system" for doing this?  The manual is very clear about what the final result should be, but not so much about how to get there.  Could/should one grease the blue steel blade?

3.) which capacitors need replacing on the wsr if wallboxes are not to be used?

4.) i have some plate voltage readings in an amp that are considerably higher than those on the schematic.  Generally, they are all about the same percentage higher.  What's a safe tolerance for this, and what would one do to lower the voltages if necessary?

5.) similarly, what's a sensible tolerance for the resistance readings in the output transformer?

I'll probably think of more.  Thanks.

[Ron Rich]

1. I use open "screw down" fuse clip holders--inside the units.
2. I have never had a problem adjusting them on an ES-11--a 10--totally different story -- Word of advise--before "adjusting" ANYTHING, on any machine, be sure ALL moving parts are "moving" as they should--clean and lubricated ! ( "Adjustments" do NOT change, in most cases, without "help" !) No as far as I can recall, no "grease" of any kind on the blue steel parts--
3. All are subject to "shorting out" -- I always replace all of them except for the .005/1000, which I just disconnect--
4. If using the specified type meter on the schematic, the specified AC input voltage, and the specified, known good, rectifier tube, they should be "right on". Other meters, voltages, 10% or so would not worry me-
5. IMHO--about the same as stated above in #4---
Ron Rich

[robnyc]

"1.) I've read both Ron and Rob describe the additional fusing of the receivers, electrical selectors and mechs. I assume you use simple inline holders, but if there's a better way..."

In Seeburgs I've only added fuses inside the selection receivers. on LV i use the typical clip type bolted to existing holes in the pan. For the 150VAC and 400DC i use inline holders for safety.

"
2.) I've found the adjusting of the Electrical Selectors' lock pawls to be maddening... " As Ron points out, these should not require much, if any, adjustment. I've only found the locking splines in the wallboxes to be even slightly tricky --and that is to keep them for releasing before the box is finished send an '0' selection. The interlocking on the V-Vl-K drums can be a pain though.

"4.) i have some plate voltage readings in an amp that are considerably higher than those on the schematic. Generally, they are all about the same percentage higher. What's a safe tolerance for this, and what would one do to lower the voltages if necessary?" This is caused by several different factors:
1) As tube emission declines they draw less B+ thus th eload on the supply declines and the voltage typically rises.

2) On some Seeburg amps the to-ground leg of the large voltage divider resistor adjacent to the rectifier-filter input can open causing voltage rise. Checking this is simple. Be sure power is off and caps discharged to avoid damage to your meter.

"5.) similarly, what's a sensible tolerance for the resistance readings in the output transformer?" IMO, DC resistance measurements in output trans is basically useless unless you are very familiar with the particular transformer and circuits. Unless a tran is radically bad with a lot of shorted turns, resistance will not tell you much. For home testing simple loud-level tests using a known-good set of output and driver tubes will usually be adequate. Defective transformers exhibit poor-distorted bass and generally lower output.

RobNYC

[nyjb]

Thanks, guys. V. Helpful.

The large voltage divider resistor is the R1, correct?

Here's a few more: what would be the best way to run two speaker cabinets from one amplifier? what kind of wire do you recommend for the tonearm? I know it has to be pliable. Is there a particular gauge? Lastly: I think Rob said he replaces the 5" speaker in some boxes with a "high-efficiency horn tweeter." Could you be a little more particular?

[Ron Rich]

Yes--R-1 is the "standee"--dual section resistor.
Do not understand what you wish to do here--external (remote) speaker hook-up is explained in the service manual--probably more details in the I and O manual for the R's.
32 gauge twisted pair wire.
Can't answer for Rob--I do not change it--
Ron Rich

[nyjb]

I meant connecting an entire additional R cabinet-- that is: 2 12" speakers, 2 8" and one 5", ideally without making any mods. It'd be like two jukeboxes running off one mech, one WSR, one amp, etc. I'll look in the manuals, but I don't recall seeing much beyond instructions for connecting the remote speakers.

[Ron Rich]

OK --I don't know if a R amp could/would have enough power to make that possible--If you don't want it too loud, you should be able to do it--

[robnyc]

Oct 3, 2017 16:10:07 GMT nyjb said:

Thanks, guys. V. Helpful.

The large voltage divider resistor is the R1, correct?

Here's a few more: what would be the best way to run two speaker cabinets from one amplifier? what kind of wire do you recommend for the tonearm? I know it has to be pliable. Is there a particular gauge? Lastly: I think Rob said he replaces the 5" speaker in some boxes with a "high-efficiency horn tweeter." Could you be a little more particular?

Each cabinet speaker system presents a load of 8 ohms to the amp. If you want to connect another 8 ohm load just turn down the "speaker watts" tap on the active amp from '20W" to the "10W" tap. Reason: two 8 ohms loads in parallel equal 4 ohms and thus attempt to draw twice as much power.

-As a general rule I don't replace whatever "tweeter" was in the oriignal system -I just add the horn and 6db crossover. A good current choice:https://www.pyleaudio.com/sku/PH25/3-x-3-Horn-Tweeter

Also, on the R the 8" side speakers were not really suited to handle the bass from a fully driven amp. I added a capacitor of somewhere around 50-100mfd (whatever was handy) to get the deep bass out of them. This also frees up a couple of db for the 12".  These 100 select models never had a real crossover and fed everything through the woofers. Nice and cheap for the manufacturer, but not great for listening. A simple bass choke of around 3-4mH in series with the two woofers (which are also in series) gets frequencies the 12" can't reproduce well out of them and cleans up the over-all sound.

RobNYC

[nyjb]

Cool.  Round 2.

I am working on some MRA5-L6s and would like to “optimize” them, or at least get a sense of how to:
a) get the best sound from them (notwithstanding that “best” is subjective)
b) avoid putting undue stress on any of the components
c) avoid overthinking

Does anyone have a good general criteria for choosing a set of bench tubes? I have an oscilloscope and basic know-how with it. Should I look at frequency response charts for each tube, and measure against that? That seems a little much, but I'd like to have a standard set to use.  I have about a dozen (of each) to choose from.

Or standard “road tests” in order to weed out troublesome ones?

Biasing. I know the grid must be negative with regard to cathode, and that output tubes should draw equally, but how else do you know if a tube is biased correctly?   Is this strictly “if it isn’t broken, do not fix it” territory? 

I understand the basic idea of impedence matching, but am a little unsure how to apply it. I have speakers with a wide range of resistance measurements. I understand that each pair should be matched. Are there other steps one might take to align speakers with the amplifier’s output?

And in reference to the bass choke of 3-4 mH that cleans up the sound in the 12” speakers: are there any other relevant specs to look for before ordering one? Where do you install it?

[nyjb]

While we're at it...

likely suspects for a gradual loss of volume?

[robnyc]

On #1: C-avoid overthinking. The amps are rated at "25watts". In reality a strong set of 6L6's will yield about 22 watts into 8Ohms at the outset of clipping. As for practical loading, I've run these amps with a 32 watt load for an extended while location renovation precluded installing an external sound system to carry the added load. Tubes are forgiving -but avoid groos overloads and shorts.

"Does anyone have a good general criteria for choosing a set of bench tubes?' that is answered by the procedure above. I inject a 1KC signal at the grid of the 12AX7 (driver-splitter)use an 8 ohm load across the output (use at least a 25w resistor). Increase level to clipping just starts. Measure the AC across the resistor and use Ohm's law to calculate the power produced. For the other tubes I just measure DC against the schematic when they are in-circuit and not driven. Extra points for also measuring the AC signal voltages.

Biasing adjusting on these fairly gentle class AB amps is not necessary and there is not much you can do in the Seeburgs anyway. On the amp used in the 201 they finally went to separate cathode resistors in the finals so you can compare current.

" I have speakers with a wide range of resistance measurements. I understand that each pair should be matched. Are there other steps one might take to align speakers with the amplifier’s output?"

ALL speaker exhibit a wide variation of impedance in relation to frequency response and that is either further controlled or aggravated by whatever support the enclosure gives at the speaker's resonance point. For this old stuff, just go by the speaker "plate ratings' -that is if it says 8 ohm -consider it so and don't worry about it.

"And in reference to the bass choke of 3-4 mH that cleans up the sound in the 12” speakers: are there any other relevant specs to look for before ordering one? Where do you install it?"

As you can see here: www.verntisdale.com/schem/mra5-l6.jpg The 12" are in-series so placing a choke at any convenient point at either end is Ok Remember that you are calculating the choke value for two 8 ohm speakers in-series so it is 16 ohms you are choosing a choke for.

Similarly, the 8" sides should have a capacitor to reduce the bass fed to them. I used approx 220mfd. Again, selected for a load of 16 ohms.

"Gradual loss of volume." How gradual-? If the 6SK7 & 6Sl7 tubes are in-circuit the AGC will have an effect. If Pin 3 on the mute female is grounded the AGC will attenuate the input signal as the input increases. If Pin 3 is not grounded the squelch voltage will build up and lower the volume. Try the tests w/out the 6SK7 tube. This assumes that the amp has been rebuilt. Otherwise leaky caps are the cause and you are risking both tubes and transformers.

Rob in Rainy NYC

[nyjb]

Rob, you are the man.

I'll try the things you suggest.

The 3 and 4 mH bass chokes I looked at online have impedence ratings and things like "current compensated."  

It's a great help, as is the coaching you've provided previously when I was grappling with the (very) basics.

i've used that resistor as dummy load before.  It gets pretty hot.  Expected?

The loss of volume was over the course of 5 or 6 hours, without the squelch or avc tubes, and on full or close to full volume.  it's not an especially loud jukebox, as it uses a redhead with new, stereo compatible stylii.  I know I've seen a modification that replaces the 5879 with a 12AX7 for some additional oomph.  Recommended?

I've tried a DS cartridge and some others too, which (naturally) deliver much more volume, but not nearly as nice a sound.  Haven't tried that with the speaker mods you suggested though.  Lots to do in rainy Brooklyn.

[nyjb]

ok, so to make sure I've got this:

the number of watts in the load is the current times the voltage.
the voltage is the current times the resistance.
therefore, the load in watts is voltage squared, divided by the resistance, regardless of the current.
In this case, the resistance is 8 Ohms, which is aligned with what's on the schematic, as the AC voltage at the speaker plug is 13.5.

In this case, the current is about 2.7 Amps.

I'm a little unclear about where to take some of the measurements though, and whether the setup is the same for the 6L6s and the 12AX7s.

By "output" do you mean the speaker socket? I assumed I'd jumper the 1 and 4 pins with the 8 Ohm resistor, and then take all the measurements across the 8 Ohm resistor. Then I started wondering if you meant the output of the tubes themselves, since it's the yield in watts (without clipping) of the tubes that I'm checking. Overthinking again, perhaps. But underthinking can have a bad outcome, too.

At any rate, it's no longer rainy here, and I appreciate the help a great deal.

[robnyc]

"By "output" do you mean the speaker socket?" Correct. You are measuring the power output to determine the condition of the output and driver tubes.

"In this case, the resistance is 8 Ohms, which is aligned with what's on the schematic, as the AC voltage at the speaker plug is 13.5.." The relevant number here is wattage. 13.5 VAC into 8 ohms is approx 23 watts.

Rob-NYC

[nyjb]

I'd like to get more volume from the MRA5-L6. I'm using redheads. Is there a sensible way to increase the value of a resistor or two without throwing the biasing off?