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speaker help Answered

I am trying to find how this speaker works and I can't. Please help me.Please respond.


That speaker is in bad shape. You would be better off just buying a new one.

hi,Im from Argentina, first sorry my english,I need help, I try to build a harp amp based on the b6rf, I make some changes and I not sure about the values, this is my schematic, can work? can change the original rectifier X 5u4? thanks and sorry again for my english


Hmmm. If you substitute a 5U4 for the 5Y3GT rectifier, you'll get a higher output voltage from the power supply. It's a heavy-duty, more capable rectifier. Assuming the power transformer is identical, of course. If you're planning on using the same tubes for the preamp and the phase inverter as the schematic (both have max plate voltage of 300V), you might have to redesign the power supply somewhat. If the 6V6GT power tubes are NOS, they can probably handle the higher voltage (even though close to, or beyond spec plate voltage.) Don't forget--U.S. line voltages in 1960 were 100V; they are close to 120V today. I realize you're in Argentina and don't have that exact issue, but probably a similar one.... Per this thread--you know the B6RF uses a field-coil speaker, right? And that the field-coil is functioning as a choke in the power supply?

Hi and thanks, about the speakear yes, I already know the way of replacing it. Here we got 220v line voltage, so the power transformer is adapted for it. The 6V6GT are NOS and I try to use the same tubes for the preamp, U say the power suply don´t work that way? what can I do? And last, the change 5U4G X 5Y3GT was sugested for a harp amp to get a higher output voltage, U think that is a mistake? What changes U suggest in the schematic? Or maybe I must do like the original and just change the filter caps x .1uf? the values for the caps and the resistor is correct in my schematic? sorry again for my english and Thanks

AFAIK, the schematic is correct (and your english is quite good.)

Regarding the rectifier change:
I really don't know the secondary voltage of your transformer. A lot of the older amps were operating right at the limits of the (NOS) tubes. With the higher line voltages today, they sometimes burn up tubes quickly.

Using a more efficient rectifier like the 5U4G will raise the voltage even more.

Have you tried simulating the power source with Duncan Amp PSU Designer II? When I quickly compared the rectifiers in a simple PS circuit, the 5U4G was 30V higher output than the 5Y3GT.

Higher voltage will have an effect on the sound. Also, I don't know if this amp is biased for Class A, or Class AB. If it's Class AB, then a more capable rectifier will tighten up the sound somewhat--give you less "sag." But some folks want that that sag for the vintage tone....

The field coil is "dual use"--it energizes the speaker and functions as a choke in the power supply. Note how it's wired between the first two filter caps in the supply.

Sorry that's a typo; should be: -U.S. line voltages in 1960 were 110V;

i am not good at electronic stuff. try posting it


10 years ago

The attached device is an output transformers. Tube amps need to convert their own output impedance (any where from 2K to 8K ohms) to the low impedance of the speaker (4 to 16 ohms.)

Virtually every tube has an output transformer. Some are attached directly to the speaker (I'm linking a pic from one of my older instructables, which shows an OT mounted on a speaker.) The secondary coil of the output transformer connects to the speaker, and is two of the wires on the speaker coil.

The speaker--it's likely an old field-coil speaker. Large permanent magnets were once quite expensive, so they used electromagnets. Here's a page describing electrodynamic speakers.

Five wires total? It's something like:

2 wires for the field-coil
2 wires for the primary coil of the output transformer (single-ended)
1 ground

Or very likely:
2 wires for the field-coil
3 wires for the primary coil of the output transformer (push-pull)

--A push-pull output transformer has three primary coil connections: a tube on each end, and the current source in the middle, on a center tap.


Now I see forgesmith has already said most of this... ops. One more thing--you don't need an output transformer for a modern solid-state amp. They can drive a low-impedance speaker directly. You can remove the OT. Unlike most inductors and transformers, the DC resistance (measure with a VOM) of a speaker is pretty close to it's inductive resistance. I.E., if you measure the voice coil and it reads 6.2 ohms, it's probably an 8 ohm speaker.... But you'd still need to energize the field-coil...

Here's a schematic of a Gibson BR6F amp. It utilizes a field-coil speaker.

I've clipped a part of the schematic. Color codes:

Blue-- primary (inputs) of the push-pull output transformer.
Red-- secondary (outputs) of the PP OT (connected to the speaker voice-coil.)
Green-- the field-coil leads (connected as a choke in the power supply.)
Yellow-- the field-coil itself.

IF the OT is a push-pull transformer, the 5 leads on the plug are blue and green...

The field-coil value is given as inductive resistance (1K ohms) rather than Henries.

Frankly, the amount of voltage needed to energize the field-coil wouldn't be very much--guessing, it's probably in the 5 - 15 volt range. The voltage differential between both ends of that LC filter (the coil and the two filter caps--marked 10 and 20) wouldn't be very large.

So you could connect the field-coil to an adjustable wallwart, and start at about 5V.

Note: You're far more likely to fry a solid-state amp (vs a tube amp) by connecting too large a load on the power (output) transistors... so be sure the speaker impedance is well-matched to the amp (and like I said before, you wouldn't need the output transformer at all...)


the amount of voltage needed to energize the field-coil wouldn't be very much--guessing, it's probably in the 5 - 15 volt range.

Hmm. Strike that... I looked up the Gibson GA-9, and it has the voltages on the field-coil ends marked as 342 and 275V--a differential of 67 volts. So the coil might need more voltage (50 to 75V ?) to magnetize the speaker core. All these values depend on how much current is drawn by the rest of the amp components.

No harm in starting with a low voltage, tho...

is there any way to make it work on a newer stereo/boom box.

If it works at all, probably not, you'd need DC for the electromagnet thus likely a different power supply than what's in the equipment. You'd have to try to get about the right voltage and amperage. It that's a transformer for the electromagnet then it wants at least a ripple current thus battery power is ruled out.

(combining other replies you made...)
Well, searching for that speaker number reveals 85015 is a Phoenix, Arizona zip code, so not much help that way. But the "i" on the chunk may stand for inductor, which would make sense if it was a transformer or choke coil. How many wires go into and out of it? If two or three from the plug go in and two go to the end of the speaker, very likely a transformer instead of a choke coil. If only two go in period, not a transformer. Now, while I have yet to encounter a 'wire wound capacitor' I will note that, depending on application, a choke coil and a capacitor can sometimes serve the same function for a circuit. Thus, I suppose, it's possible what normally would be called a choke coil could be referred to as a wound capacitor. (ugh...)

Red to center? Huh. Are any of them attached to a metal housing? That would be a ground.

Besides, what did the linked Wikipedia article say?
The quality of loudspeaker systems until the 1950s was poor.
The paper on the cone is already going to heck, probably wouldn't sound good at all, and not for much longer anyway.

i got the numbers worng i posted the right numbers in a comment below

Well, the numbers are the same which indicates everything was built together as a unit, same number was simply stamped on in two places. But it's not helping on the web search, all that's coming up for B5015 is it being used as an identification number for a dozen different things, and I have no other possible speaker references. Sorry.

Well that is quiet the old peice of history you have there. What exactly did that come out of? Looks like it came out of an old electric organ or perhaps one of those old (1940's-1960's era) fireplace/speaker combo cabinets as it has similar prongs to some speakers I found within said cabinet, however it wasn't actually that old. As to that device, as far as I'm concerned that's a transformer or a rather old style hand wound capacitor. The later would make more sense as it would be used to cap the high freq. end of the audio, however the fact that there are 5 leads is fairly perplexing. And henceforth, it is most likely a transformer as the additional 3 leads would be for the secondary/primary coils, ect. Again I can't give much input on this either as the pictures are kind of vague. Any chance of getting some part numbers off either of these? And I'ma put this one out on the limb and ask a dumb question, is the transformer connected to the speaker in any way? Or is it just there for sake of space saving (would be rather odd to mount a transformer there, however it may have been for added effect of cooling from the speaker). Oh and the dome (otherwise known as the dustcap), the diameter of aged paper shows it'd be a rather small dustcap for a speaker this size, it was more likely a funnel shaped cap that pointed outwards (couldn't find a picture on google but I got a speaker round here somewhere that has one). A rather interesting find my friend, and yes, I am the stereo master around here, I know too much about speakers..*cries self to sleep*

i had found it in my attic. and there are 4 wires that connect to the speaker. the speaker number is 85015 the capacitor number i8515.

corectioin on numbers speaker-B5015 cpactior-B5015

O::::::::::::::::::::O :::::::::::O-red ::;:O::::::::::O-black

Yes, it looks like the tiny dome is gone. Going from the plug (and what little I know about audio equipment) it might be an old PA system speaker, the plug is like the old "vacuum tube base" connectors, seen those before. The center prong is possibly ground. The chunk is likely an impedance matching transformer. How much magnetism does it have now, is there a permanent magnet? If not, two of the wires might have been DC and going to an outside coil on the end while the voice coil is on the inside; near as I can make out from the pics that would be red (+) and black(-) for DC while the bottom wires went to the voice coil.

From the Wikipedia loudspeaker article:
These first loudspeakers used electromagnets because large, powerful permanent magnets were generally not available at a reasonable price. The coil of an electromagnet, called a field coil, was energized by current through a second pair of connections to the driver. This winding usually served a dual role, acting also as a choke coil filtering the power supply of the amplifier to which the loudspeaker was connected. AC ripple in the current was attenuated by the action of passing through the choke coil; however, AC line frequencies tended to modulate the audio signal being sent to the voice coil and added to the audible hum of a powered-up sound reproduction device.

By the diagram on Wikipedia the tiny dome was just a dust cap, not really needed, until fine crud ruins the voice coil windings.

So DC on red & black, center ground, and other two for voice coil would make sense. If the chunk has the other two wires then it's impedance matching, if the red and black then, umm, I don't know, choke coil?

Yep I'm with forgesmith on this one it looks like PA equipment, the transformer is more then likely a 70 volt input, and being five wires it's a multi-tap so you can select from four different output wattage / volume, which is fairly common in high voltage pa systems ??????