speaker help

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

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grundisimo6 years ago
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.
gmoon gmoon9 years ago
Sorry that's a typo; should be: -U.S. line voltages in 1960 were 110V;
Sun Gear (author)  martin truco9 years ago
i am not good at electronic stuff. try posting it
gmoon9 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.
gmoon gmoon9 years ago
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...
gmoon gmoon9 years ago
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...)
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