Westrex model 26c Very Poor sound.

Kenjs

Member
I have a couple of Westrex Model 26c amps I am working on. They were recently update with Nichicon polypropylene caps through out by somebody in Knoxville, TN. The owner said the cap update made the amps sound terrible. The upgrader gave the owner 4 paper and oil caps and told him to replace C8 and C9 with these pio caps. Made no difference in sound. The sound is hollow, lacks all bass. Basically they sound like transistor radio. Heavy transistor radio.
they both have the original 1614 tubes. A mix of 12au7 and 12ax7.
I cannot find schematic for these.
Any one have an idea why these things lack bass and sound like s...t. Also low volume. I have to turn up the volume on my VTL 2.5 to almost 12:00 to get a reasonable volume. Any help would be greatly appreciated
 
I doubt the problem is the capacitors unless incorrect values were used or the upgrade resulted in a wiring problem somewhere in the circuit. First thing I would suggest is getting those tubes tested...or replace them with known good tubes. What is the rectifier tube? Also inspect the wiring for any signs of shorts or poor connections. Are both amps identical and do they sound equally bad?
 
Is this Westrex a McIntosh in some way? I don't recall there was a relationship between the two?

Any pics available?

Cheers,

David
 
Westrex model 26C

Hello !

David take a look on my pictures , they are coming from a "mint unit " never touched ! rare no ?
 

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The rectifier tubes are 5U4G. Both amps are identical and it's strange both sound equally bad.
The amps are labeled Westrex model 26C 30 watt power amplifier Macintosh laboratory type A-123. The customer gave me sckhmatics for a Macintosh MC-30 power amplifier and said the circuits are the same.
I'll attach photos later.
 
The customer also mentioned he wanted the old capacitors replaced in the update to be put back in the amps. He is not a happy camper.
 
Power output tubes are 1614 , there is 2 x 12AX7, 1 x 12AU7, and 1 x 12BH7

Are the input transformers in place with no adaptation ?
 
Hi Clinic-Audio,
I believe that's the tube set. I'll check for sure. I do know different brand tubes are used in each amp. The 12AU7 in one amp are different make. Nothing matches. Not quite understanding the input transformers without adaption? Do you mean the AC line voltage is set to 120 vac.
 
Not quite understanding the input transformers without adaption?

If input transformers are in place = good !
If not they will try "adaptations " or " home modifications" = not good

that's what I mean .

Regarding the power voltage they are ALL in 110/117 V .

Does somebody touch something on the board inside ? If yes , I can send you in MP some pictures about what and how the components should be
 
As I remember one of the output transformers was bad, had an open cathode winding that I did a partial jump out to make work, told him about it. I had researched on getting the transformer rewound but nobody would touch them since they are hermetically sealed transformers.
I have a feeling that the output transformers were special wound for Westrex and are not the same as a MC30, thus the difference in sound.
 
Thanks Beowulf for the schematic. Dewickt the owner did mention this about the transform and I see the jumper. I cannot believe that both amps can sound bad. The only common thing is my VTL.bpreamp I am going to use another preamp and see if that changes things I am also going to look more closely at Beowulf schematic.
Thanks.
 
Is your preamp output going directly to R1 (100K pot) with the wiper connected to the grid of (pin 2) the input 12AX7? If it is connected to the 600 ohm input, that could account for the problem as you would be drawing too much current from your preamp.
 
it's connected to the only rca jack. From the drawing, it's hard to see, but I think so. What would be the correct connection? I turned the gain up probably over driving the whole thing.
 
Yes, I believe that is the correct input...looks to be rated at 0.5V input signal. Confirm that the signal goes directly to the gain control and onto the grid of the 12AX7.
 
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Westrex 26C pictures

Ok what I have found common in both amps
1. The green wire from pin 6 of input xformer is cut
2. The jumper wire label 2 in the picture has been cut.

The resistor between pins 3 & 4 and 4 & 3 of the 1614 read
Amp1 red / violet / silver 14.1.ohms
Brown / green / silver 1.1 ohms

Amp2
Red / violet / silver 2.9 ohms
Brown /green / silver 1.7 ohms
Are the reading right? If there resistors they aren't.

The 0.5v input on back goes through a .1uf cap to on side of the pot the other side out to ground. A 220k resistor in parallel with the .1 uf poly cap. The wiper goes to the grid of the 12AX 7. Pin 2.

I still want to try another preamp. I have a Hafler 101 I'm going to try.
 

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Westrex 26C pictures
Ok what I have found common in both amps
1. The green wire from pin 6 of input xformer is cut
2. The jumper wire label 2 in the picture has been cut.

The resistor between pins 3 & 4 and 4 & 3 of the 1614 read
Amp1 red / violet / silver 14.1.ohms
Brown / green / silver 1.1 ohms

Amp2
Red / violet / silver 2.9 ohms
Brown /green / silver 1.7 ohms
Are the reading right? If there resistors they aren't.

The 0.5v input on back goes through a .1uf cap to on side of the pot the other side out to ground. A 220k resistor in parallel with the .1 uf poly cap. The wiper goes to the grid of the 12AX 7. Pin 2.

I still want to try another preamp. I have a Hafler 101 I'm going to try.
 
I would match it to a MC30 schematic which means Jumper # 1 and 2 should be bypassed and the feedback network returned to that on an MC30. Also install new 6l6Gc output tubes as lose the 1614s as they are inferior and probably worn out.
If the feedback was modified to limit frequency response to the telephone curve this would explain the sound you describe. The output transformer is the same as MC30 so with good tubes it should sound the same.

Thanks,
Ron-C
 
The resistors between pins 3 & 4 of the 1614s are not present between the plate and screen of the 1614s on the schematic? Can you post pictures? They may be parasitic stopper capacitors:


Red + Violet + Silver = 27pf 10%

Brown + Green + Silver = 15pf 10%

Perhaps clinic-audio can comment as they appear in his photo posted above?
 
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Beowulf62- yes they are capacitors. Before my time I guess. I tried the Hafler and no difference. Still would like know why the green wire at pin 6 of the input transformer is cut and the jumper cut. It difficult to see the drawing where the input comes in.
 
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