Ampex 6446 Cinemascope amplifiers

[radioactive]

Any markings on the output transformer ?

 

[soundmotor]

200w each amp nice

Well, they aren't class-A at that rating are they?

 

[soundmotor]

Any markings on the output transformer ?

Ampex often used Triad in their tube amps. The output terminal style looks like that of their HSM type but not the usual color.

Those tend to be dark brown, sometimes black or a mint green. I may have seen a tan one before but would not place a bet on it.

 

[soundmotor]

Does anyone know how the output transformer should be wired for 4,8,16 ohms? I am wondering what impedance the amp is set up for now.

Without a schematic you need to get in and measure DCR across some pins then make some educated guesses. You have 7 likely pins on the secondary side, 2 of which are tied in. My gut says the orange & yellow are for load while red & blue are feedback(?). Trace them from the transformer to end termination to confirm. The green (B+?) and the ones flanking it are likely for the tube plates. Again, trace back to confirm then ignore them. You would need to unsolder the secondary side then start measuring.

The secondary side will be a bit tougher. If you are lucky you have a single secondary winding tapped top to bottom. One end is 0 the other for high-Z loads. In between them are your various other loads. The one next up from 0 will have the lowest DCR (~.1-.3 ohms) and may be the 4-ohm termination. The one farthest away will the highest ~40 ohms+ and may be a 150-ohm+ or constant voltage secondary. From there it is a matter of orienting and figuring out what the rest are. It could also have 2 secondary windings and perhaps even a ground shield lead to cypher out. You can usually figure it out by DVM measurement then filling in the blanks on a hand drawn transformer schematic. Repeat your measurements until they orient with the terminals in logical order for an output transformer.

I may have omitted a step but someone will append if so.

 

[mike567]

Looks like you have selium rectifiers that should be replaced before they let out the magic (and toxic) smoke.

 

[Palustris]

Looks like you have selium rectifiers that should be replaced before they let out the magic (and toxic) smoke.

Yes, you are very brave to power those up with the selenium rectifier and old caps. If those coupling caps leak DC then the output tubes can draw enough current to destroy the output transformer.

 

[Potato_Head]

Any markings on the output transformer ?

Hello Radioactive - no no markings on the transformer. There are numbers next to the pins to identify them but nothing else. I have found only two other pairs of this amp in all of the Internet. None have labels on the transformers. I read a posting where supposedly 4 (pair?) were ordered by someone in Florida back in the day. All of my leads have run cold though.

 

[Drummerboy2]

Does anyone have any information on the Ampex 6446 Cinemascope amplifiers?

I just found two. They sound good but I need to know what impedance they are for better speaker matching.

Thank you

Ampex 6556 violet and neon

• Potato_Head
• Jan 30, 2017

Nice Glow

Ampex 6556

• Potato_Head
• Jan 30, 2017

Wow, that rectifier is bright! Is that normal?

 

[Potato_Head]

Ampex often used Triad in their tube amps. The output terminal style looks like that of their HSM type but not the usual color.

Those tend to be dark brown, sometimes black or a mint green. I may have seen a tan one before but would not place a bet on it.

Hello Soundmotor - thank you for the information and tips. The 6446 on the Antique Radio website has tan based transformers. The picture is too lo res to be very helpful. I did just find other examples tonight on a Japenese and a Taiwan site. I can see the numbers on the transformers but again the images are lo res and I can't make out the numbers. If I was familiar with the Ampex numbers I might be able to make a guess. I'll try to post the pictures later in case someone else can help.

 

[Potato_Head]

Yes, you are very brave to power those up with the selenium rectifier and old caps. If those coupling caps leak DC then the output tubes can draw enough current to destroy the output transformer.

Hello Palustris and MIke567 - I agree. While the amps have been relatively quiet, one is starting to make that 60 cycle hum more loudly. I should have my 1958 Pioneer amp mid week. I'll then be looking to get these recapped. I'll probably be in search of 2 sets of quad matched 807 tubes. I'm thinking that all four are biased together.

 

[Potato_Head]

Wow, that rectifier is bright! Is that normal?

Hello Drummerboy2 - the bright red tube and the 4 violet tubes are for voltage regulation. The red one uses Neon gas and the Violet ones use Argon. Bright discharge is dissipating excess voltage. When there is a low bass note that requires more power you will see the rear two violet tubes dim. If the volume is too loud all four violet tubes dim - not good sound then.

 

[Potato_Head]

Here are the new pictures that I found on Japanese and Taiwanese sites. Do the pictures of the output wiring or transformer numbers look familiar to anyone?

Seems there were at least 2 versions of this amp. Mine has steel "feet" added to the transformers. I do not have the tube base clamps and the chassis layout is different.

Japanese 6446 201205060043363830

• Potato_Head
• Feb 13, 2017

Japanese 6446 201205060041243058

• Potato_Head
• Feb 13, 2017

Can anyone read the transformer numbers?

6446_501963

• Potato_Head
• Feb 13, 2017

6446 In Taiwan

• Potato_Head
• Feb 13, 2017

 

[arts]

Potato_Head,I was looking at the photo's in you member media and came across a Pioneer that looked awfully familiar. Is that a SM-C800?

 

[Potato_Head]

Potato_Head,I was looking at the photo's in you member media and came across a Pioneer that looked awfully familiar. Is that a SM-C800?

Hello Arts - I am not sure. Just like the Ampex amps, the previous owner took some liberties with his restorations. I saw an amp that was identical to mine on ebay and a Canadian audio site. The seller was from Vietnam. I posted his pictures in my thread as well. My amp has the perforated cage, side panels and tubular handles deleted. The meter that was center mounted on the cage is now mounted to the bottom chassis. The Stereomaster logo has been relocated from the right side of the cage to now below the meter. I just did a quick search on the web and didn't find anything on a Stereomaster SM-c600. Do you have any pictures or literature on it for comparison?

The output of my Pioneer amp is dual mono with what I think is a main power switch and then two separate switches for each side. The preamp portion seems combined if I remember correctly.

 

[arts]

Hello Arts - I am not sure. Just like the Ampex amps, the previous owner took some liberties with his restorations. I saw an amp that was identical to mine on ebay and a Canadian audio site. The seller was from Vietnam. I posted his pictures in my thread as well. My amp has the perforated cage, side panels and tubular handles deleted. The meter that was center mounted on the cage is now mounted to the bottom chassis. The Stereomaster logo has been relocated from the right side of the cage to now below the meter. I just did a quick search on the web and didn't find anything on a Stereomaster SM-c600. Do you have any pictures or literature on it for comparison?

The output of my Pioneer amp is dual mono with what I think is a main power switch and then two separate switches for each side. The preamp portion seems combined if I remember correctly.

Unfortunately,I had my SM-C800 a long time ago.It is in fact a true mono design,and a very good one.Mine was so trashed (but complete and still working!) and rusty that I stripped it and scrapped the chassis. I still have the output transformers,chokes,power amp circuit boards,knobs,controls and one power transformer. Believe it or not,at the time I actually got a copy of the schematic (still have that too!) from the old Pioneer Service Center here in Montreal.Today I really wish I had kept it together

 

[Potato_Head]

Unfortunately,I had my SM-C800 a long time ago.It is in fact a true mono design,and a very good one.Mine was so trashed (but complete and still working!) and rusty that I stripped it and scrapped the chassis. I still have the output transformers,chokes,power amp circuit boards,knobs,controls and one power transformer. Believe it or not,at the time I actually got a copy of the schematic (still have that too!) from the old Pioneer Service Center here in Montreal.Today I really wish I had kept it together

Hello Arts, Thank you for the model ID. When I saw that I made a typo in my searching (sm-c600) I did a new search. Bingo! The SM-c800 is what I have. I was also able to find the Pioneer books of schematics. Are you going to build the amp? If not send me a PM and let me know what it would take for me to get the parts from you.

Thank you!!!

 

[toxcrusadr]

If you're getting an increasing level of hum, I wouldn't even put power to those until they're gone through. Rare amps and if you fry an unobtanium transformer, you're going to regret it.

 

[Potato_Head]

If you're getting an increasing level of hum, I wouldn't even put power to those until they're gone through. Rare amps and if you fry an unobtanium transformer, you're going to regret it.

AGREED!!! The change was pretty dramatic the other day. I haven't listened to them since then. I'm going to mothball them tonight so that I won't be tempted. I've got a Harmon Kardon A-500 that I can use until the Pioneer SM-C800 is done.

I'm not looking forward to moving the Ampex's though. Heavy and bulky. Uggh

 

[rave0035]

I have nothing to add, except that this is a beautiful amp that deserves to be used and displayed.

If you'd like to send it to me as a Valentine's Day present, I'd happily pay shipping.

Mike

 

[Potato_Head]

Unfortunately,I had my SM-C800 a long time ago.It is in fact a true mono design,and a very good one.Mine was so trashed (but complete and still working!) and rusty that I stripped it and scrapped the chassis. I still have the output transformers,chokes,power amp circuit boards,knobs,controls and one power transformer. Believe it or not,at the time I actually got a copy of the schematic (still have that too!) from the old Pioneer Service Center here in Montreal.Today I really wish I had kept it together

Hello Arts, I received my SM-c800 from the shop yesterday. It sounds very good. there is low level noise. I was told that this is due to the chassis having the same ground as the transformers and tubes. I can live with it though! Do you still have the meter? My meter has a short in it.