Pioneer SA-6700 - lamps are dim ... why?

[robitaille03]

Bought a Pioneer SA-6700 amp and SX-6700 tuner off Craigslist for $60, which I felt was a bargain despite the knowledge that the meter lamps in the amp were not working. I bought a couple of replacement lamps from AK's lamp guru dwojo. The originals were 55mA, 8V lamps, and I replaced them with 100mA, 8V lamps. The new ones light up, but they are much dimmer than the signal and tuning meter lamps in the tuner. I now have also noticed that the power lamp in the amp, which is identical in the tuner, is also much dimmer than its counterpart.

Anyone have any initial theories on what may be causing this? I appreciate any feedback.

 

[cademan]

Try other lamps! Measure the voltage at the lamp sockets to make sure they are 8volt! Look at the signal and tuning meter lamps and try to find some identical replacements!

 

[markthefixer]

Bought a Pioneer SA-6700 amp and SX-6700 tuner off Craigslist for $60, which I felt was a bargain despite the knowledge that the meter lamps in the amp were not working. I bought a couple of replacement lamps from AK's lamp guru dwojo. The originals were 55mA, 8V lamps, and I replaced them with 100mA, 8V lamps. The new ones light up, but they are much dimmer than the signal and tuning meter lamps in the tuner. I now have also noticed that the power lamp in the amp, which is identical in the tuner, is also much dimmer than its counterpart.

Anyone have any initial theories on what may be causing this? I appreciate any feedback.

I know EXACTLY what is happening. In the sa-6700 there ISN'T a specific transformer winding for 8 volts, so there is a transistor circuit set up to make the 8 volts needed. This ISN'T a nice regulator like it would have been SMART to do, but rather something tailored for a specific load, like 2 x 55mA. At 2x100mA it isn't delivering the correct voltage to the meter lamps. Thus they are dimmer.

THEN to add INSULT to injury, they set up another "regulator" circuit to drive an itty bitty LED for the power indicator, and that transistor Q3 will deliver 0.6v less to it's emitter and the LED/resistor than whatever the base voltage is. GUESS what they use to drive the base voltage? Yes, they used the voltage from the meter lamps which has been drawn down by the wrong lamps excessive current draw...... shudder.....

 

[Blast]

Yes, the 100ma lamps are pulling more of a load so there is a resistor somewhere that is getting a little warmer for it.

Consider yourself lucky, however. My Realistic SA-700 has a 50v pilot lamp driven directly from the B+ on the main filter capacitors. Try find a 50v lamp! ARRGH!

 

[markthefixer]

It's far more than a resistor....

First we have a series of THREE 62 ohm 2 watt resistors (R100, R101 & R123) that under the correct load drops -40v to -20v.

Next there's Q15, the 2sb507 PNP power transistor who's collector is connected to the -20.
Q15's base is connected to a -10v point generated by a dual 1.3k ohm (R97 & R98) voltage divider connected to a -20v raw dc voltage itself derived from the balancing of loads.
Q15's emitter has a 15 ohm series resistor (r124) then connected to the grounded lamps.
BUT to COMPLICATE matters, the point between the 15 ohm series resistor and the lamps is tied BACK to the base of Q15 with a 2.7v zener diode. Completely destroying any hope of any real voltage regulation. In fact it makes it very load dependent.

translated: get the 55 ma lamps. you'll have a complex re-engineering job of the circuit to make it work with more current, IF the current is even available from upstream.

 

[robitaille03]

Yes, dwojo and I decided to go with the 100mA lamps because 55mA's are impossible to find. Guess I'll have to settle for dim lamps?

 

[Blast]

Yes, dwojo and I decided to go with the 100mA lamps because 55mA's are impossible to find. Guess I'll have to settle for dim lamps?

I actually got tired of how bright the bulbs were in my SA-2000 so I upped them from 8v to 12v so they'd dim slightly.

I assume you've checked Parts Express. I also assume that these are axial lead bulbs you need? I don't know anything about the construction of the amp but do you think you could get another STYLE of lamp to fit? PE has some 35ma and 70ma bulbs in other styles and voltages maybe you could experiment around with.

 

[robitaille03]

Lamps dim ... and ...

Sorry for the four-month delay in responding ...

Yes the lamps are axial-lead. And they're packaged pretty tightly inside of the meter "compartment" - a small little plastic box held together by thin pieces of metallic tape - so switching the lamps out for a different kind would require pretty much an absolute identical shape/length/circumference.

I've kinda gotten over the fact that the lamps are dimmer than the ones in the matching TX-6700 tuner ... just in time to notice that the right channel has an intermittent very audible "crackle" to it. Anyone know about this problem? Does it sound like something that can be solved with deoxit, or does it sound like something more involved ... like a recapping project? Deoxit I can do; recapping is outside of my scope ... at least for now.

 

[jdurbin1]

How about something like this:

http://www.atlantalightbulbs.com/ecart/10Expand.asp?ProductCode=7134

with a resistor in series? Should be able to get the equivalent wattage out - more or less - with a lower voltage lamp wired in series with the right value resistor. You want to get roughly just under half a watt of output while not exceeding the design current of about 55ma.

I didn't look at the physical dimensions but seems like this kind of solution would work.

John

 

[robitaille03]

Thanks John. Adding resistors and such is outside of my scope of ability. Perhaps I should start a thread asking for recommendations for books on basic electronics ... it really bugs me that I can't fix these things myself!

 

[Switchblade]

Use LEDs......

 

[redd6054]

How I solved this problem on my 3 SA7700's and 3 TX6700's is to use 8volt 50mA grain of wheat bulbs with bare wire leads. I spread the leads very carefully and soldered each one to the solder pin with the bulb pionting straight up. It gives a nice yellow 70's glow and the bulb is not visible when you put the shiny silver back on. Looks perfectly retro. I tryed LED's , I did not like the look at all.!
cheers Wolfgang

 

[Jim Mas]

15 year update for those who may be interested in or still dealing with this problem of dim meter lights and/or LED power indicator on SA-6700/7700. I have SA-6700, SA-7700 and TX-6700. The SA-6700 has original lamps working fine. The SA-7700 VU meter lamps and LED power indicator all are dim. Don't know if the LED has anything to do with the meter lamps. I installed new commonly available 8V 100 mA replacement bulbs at the meters - still dim. I borrowed an original 55mA lamp from the TX-6700 (don't like how the green condom hue doesn't match the natural of the dial indicator, anyways) and installed on the SA-7700 with results showing no improvement. Tinkering with measuring voltage at the meter light posts will probably result in a catastrophe, for me anyways. But if anyone had success with repair the voltage regulation on these models, please let me know - is it worth having a pro take a look? Real world problems lol...

 

[WestCoastDan]

The dim bulbs are probably due to incorrect bulbs installed at some point. I tried several different LED and incandescent bulbs before finding this thread and getting the exact spec bulbs. As someone said above:

"get the 55 ma lamps. you'll have a complex re-engineering job of the circuit to make it work with more current, IF the current is even available from upstream."

Available here:

10 x 8V 55mA 0,055A 0,44W / Axial Glühlampe Lampe Bulb Lamp / T1.25 / 4mm x 20mm | eBay

Speziallampen und Ersatzteile für klassische HiFi Geräte. 8V 55mA / 0,44W. Diese sind nicht für die Verwendung im Haushalt geeignet und dürfen z.B. nicht als Raumbeleuchtung verwendet werden. Reparaturen an elektrischen Geräten sind gefährlich und dürfen nur von Fachpersonen durchgeführt werden!

www.ebay.ca