Author Topic: Pioneer SA-400 Valve Amp Repair  (Read 1767 times)

Offline Bruce M

Pioneer SA-400 Valve Amp Repair
« on: March 13, 2018, 11:17:47 AM »
Hello All

I have an old Pioneer SA-400 valve amp that my father bought in about 1966, along with a Lenco L70 tt, which is still playing very well.

About 10 years ago he tried to revive the little amp from years of storage. He seems to think he changed the valves, but it just plays at very low volume. I must admit I have not tried it out myself yet.

The question is, can anyone recommend someone to look at repairing this for me, I'm in Cape Town?
And further to this, would it be worth it?

At a claimed 11 watts per channel (old school watts though...) I would just like to use it in a small study with some small bookshelves.

Below is some info from Vinylengine, and they also have the wiring schematic:

Power output: 11 watts per channel into 8Ω (stereo)

Frequency response: 30Hz to 20kHz

Total harmonic distortion: 1%

Damping factor: 13

Input sensitivity: 2.3mV (MM), 38mV (ceramic), 150mV (line)

Signal to noise ratio: 60dB (MM), 80dB (line)

Speaker load impedance: 8Ω to 16Ω

Valve complement: 12AX7, 6BM8

Dimensions: 352 x 260 x 135mm

Weight: 7kg

Year: 1967



Thanks,

Offline Family_Dog

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Re: Pioneer SA-400 Valve Amp Repair
« Reply #1 on: March 13, 2018, 01:39:55 PM »
Definitely worthwhile!

It will need new caps, if that has not yet been done. Ask Andre (Kent Kassler) on the forum, he should be able to recommend someone.


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Offline JonnyP

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Re: Pioneer SA-400 Valve Amp Repair
« Reply #2 on: March 13, 2018, 02:18:17 PM »
It may be that the speakers are low sensitivity as well.  What is it running?  You need pretty sensitive ones for an old valve amp to get any real volume out.
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Offline Mars

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Re: Pioneer SA-400 Valve Amp Repair
« Reply #3 on: March 14, 2018, 03:31:25 PM »
Thanks for the thread, JohnnyP.  I have a SA400 on the table too; and the volume is low.

Power supply caps have been replaced, as well as the coupling caps. Volume still is low. I have ordered ECL82 tubes, hoping that is the reason for the bad performance.
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Offline Kent Kassler

Re: Pioneer SA-400 Valve Amp Repair
« Reply #4 on: March 14, 2018, 05:08:15 PM »
impedance switch on the rear....?...it causes nonsense like this sometimes.
« Last Edit: March 14, 2018, 05:10:45 PM by Kent Kassler »
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Offline Mars

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Re: Pioneer SA-400 Valve Amp Repair
« Reply #5 on: March 15, 2018, 05:16:46 PM »
Thanks for the thread, JohnnyP.

Apologies for calling you by another name, Bruce M :-[
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Offline Bruce M

Re: Pioneer SA-400 Valve Amp Repair
« Reply #6 on: March 16, 2018, 11:26:25 AM »
Hello Chaps, thanks to all for the input.
I have left it with John Gilmore here in CT, lets see what he says once he's had a chance to look at it.
The comment on the sensitivity of the speakers is probably very valid. I'm actually looking for a set of small bookshelves with high sensitivity to run in a small study with this amp, if it can be resurrected!

Offline Ampdog

Re: Pioneer SA-400 Valve Amp Repair
« Reply #7 on: March 19, 2018, 04:03:49 AM »
Just a late comment, Bruce,

By valve complement, did you just mean which different types?  A stereo 11W/channel will need 4 x 6BM8 and 2 x 12AX7 at least, if my guess is correct.
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Offline charles

Re: Pioneer SA-400 Valve Amp Repair
« Reply #8 on: March 19, 2018, 01:28:54 PM »
According to Philips Electron Tube manual, Volume 1 (1964) .

ECL82/6BM8 output in class AB push-pull = 10.5 Watt @ Va= 250VDC

Offline Ampdog

Re: Pioneer SA-400 Valve Amp Repair
« Reply #9 on: March 22, 2018, 02:46:16 AM »
I may have been somewhat misunderstood: I meant 4 x ECL82 etc. for a stereo amplifier.

Then one must just remember that figures listed in valve manuals are for the valves only, viz. at the vanve anodes.The output transformer efficiency must still be taken into account. (Because of the variety of OPTs on the market valve data cannot include that.) This usually about 85% to 90% for typical transformers in that class.

10,5W would thus configure to  some 8 - 8.5W at the loudspeaker terminals. Also, this is with an ideal power supply (no 'sag' at maximum output).

Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline afroaudio

Re: Pioneer SA-400 Valve Amp Repair
« Reply #10 on: April 04, 2018, 05:06:20 PM »
I also have one of these, I have intermittent level dropping which I think is related to dirty switches or pots.. has been recapped.. must investigate further as its a nice little amp for efficient speakers!

Offline Bruce M

Re: Pioneer SA-400 Valve Amp Repair
« Reply #11 on: April 05, 2018, 10:43:48 AM »
Hello All

Just an update on the old Pioneer, I've had it recapped/serviced and it sounds good. Unfortunately I got it back the day before I went away, so only had an hour or so to test.

I'm running it in a small study driving a set of new Klipsch bookshelves with a claimed efficiency of 94 dB, so it's plenty loud.

Many thanks to John Gilmore here in CT (as recommended by Kent Kassler, thanks) who worked the magic on it. Highly recommended.

Using a Yamaha Musiccast streamer (playing FLAC from Tidal) as a source, so definitely a new school/old school setup.

Thanks to everyone for the input.

Offline afroaudio

Re: Pioneer SA-400 Valve Amp Repair
« Reply #12 on: May 05, 2018, 04:23:53 PM »
Hi Bruce

Keen to hear more! Do you have any pics you can upload? I must ask John what he did on yours and must find time to work on mine again.

Offline Bruce M

Re: Pioneer SA-400 Valve Amp Repair
« Reply #13 on: May 29, 2018, 01:31:25 PM »
Hi Afroaudio

Apologies for the late reply, life happens.

I just figured out photobucket, so lets see if this works!






« Last Edit: May 29, 2018, 01:48:06 PM by Family_Dog »

Offline Family_Dog

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Re: Pioneer SA-400 Valve Amp Repair
« Reply #14 on: May 29, 2018, 01:44:01 PM »
Bruce, you forgot to add the [ img ] tags - I added them for you.

Edit: But just noted the last three pics are one & the same?

-F_D
« Last Edit: May 29, 2018, 01:49:00 PM by Family_Dog »



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