Orignal '65 Fender Blackface Deluxe - Low bass .. .muddy.

[RetroTone]

Hello,

So.. about 6 months back.. I picked up a '65 Deluxe Reverb (NOT RI)... I was told before it was sent to me that the amp lacked bass. Anyway... know I am about to dive into the amp and see if I can sort it out.

This is the issue... amp lacks bass response... with the bass pot on 10 and treble on 0 amp still has not sufficient bass response. In general.. the amp just does not sound great. Does not have that Fender chime.

THIS is what I have ruled out

-Problem is in BOTH channels.
-NOT Tubes or Bias. All new tubes and bias checked.
-NOT speaker - Tried a couple different speakers
-NOT FILTER or BYBASS CAPS. ALL new Electroylitcs in the amp.
-NOT the pots.

The amp has sufficient volume (at least I think it does).. so I am assuming it is not a power issue. Then again.. I could be wrong. Any ideas on which direction I should be heading? Thanks in advance for your response!


Greasy D'

[imaradiostar]

Inject a signal at the input of the phase inverter- see if the problem persists.

Perhaps you could connect the amp to a dummy load and see if it has linear response from approx. 80 hz up to 5k or so. Do you have a signal generator, resistive load and voltmeter?

jamie

[kenda47]

Hi RetroTone.

All the things that you say above are definitely ruled out, did you do yourself or were you told they had been done? If you did and are happy here is where I think you should be headed. If this is an original it is nearly 50 yrs old! You say it has had new filter and bypass caps. Great but have the coupling caps been replaced? If not then at least one or even all of them will be leaking which will mean very poor tone. On an amp this age if it came to me for repair I would replace every cap including coupling caps in the amp period. These vintage amps are easy to work on and If this does not bring your tone back to life let me know and I will think again.

[RetroTone]

Hi Kenda,

Thanks for your response. Coupling caps have not been changed. That was my first hunch BUT.. as I was having the same issue on both channels.. I assumed it was not the problem. I didn't think it likely that all coupling caps would need to be changed. A friend of mine who builds amps told me that its not common that the Blue Molded caps need to be changed and that it was best I leave them unless tested bad. What is the proper way to test for a bad coupling cap? As the amp is pretty much stock , I would hate to rip out all the coupling caps just for the sake of adding new ones, unless it is necessary. Thanks in advance for your response!

Greasy D'

[Twist]

Without a signal generator or scope you might check all the voltages on the phase inverter tube with your multi meter. Also you may have a faulty speaker transformer.

[RetroTone]

Unfortunately, I do not have a signal generator or scope. I will go and check the voltages on PI. I was thinking about the transformer being faulty. What is the best method to check the output transformer?

Greasy D'

[Prairie Dawg]

Output transformer is a very simple device. With power off and caps drained test pin three to B+ on both power tubes and they should be about the same-that's the primaries. Test for continuity from the speaker side. That's the secondaries. Best way to test is to sub a known good one into it.

It's time to get back to fundamentals.

You bought this amp with a known problem and from what you've said this was a problem amp that somebody gave up on.

Basic troubleshooting theory suggests that 95 per cent of what's wrong in anything is traceable to what the last person inside did in an attempt to do whatever.

Unless you have personally verified the bias to be correct and the tubes reasonably matched, recheck. At typical DR voltages @450vP you should be seeing about 20ma each with a cathode current checker.

Unless you have personally validated that the speaker's working right, do not assume from what the seller has told you that it's right.

Get a schematic and start marking off everything you have personally checked and therefore know is good.

Did you put the 'lytics in? If not, replace them anyway-ALL of them- because they're cheap and you haven't eliminated them. I just rehabbed a DR that had "new electrolytics" put in a year ago. But they were 25 year old blue Mallorys that were [probably found in somebody's tube caddy. As someone here says all the time-never make up an excuse not to check something.

Now, you're ready to start validating resistances. Carbon comps change value over time so check 'em against the schematic.

Once you're done with that you can think about capacitors. They're easy enough to swap and I'd change the grid coupling caps (.022 or .1s) for testing purposes and you can always put the old ones back in. There are only about 4 or 5 caps past the preamp sections. Also while you're checking, check the 470 ohm and 1.5k ohm resistors mounted in the power tube sockets-they get cooked.

Now, you've got a baseline of known good parts to work from, and you can start checking voltages-that should take about ten minutes.

If you're still not having any joy it is time to start looking at stuff like bad solder joints and probing with a chopstick or dowel.

Look at it this way-your problem is located in a chunk of real estate that measures 10 x 18 inches more or less. It is there. You will find it.


If the problem's in both channels it's downstream of the preamp sections and should be fairly simple to localize because there's not much left to that amp.

[Raybob]

...Basic troubleshooting theory suggests that 95 per cent of what's wrong in anything is traceable to what the last person inside did in an attempt to do whatever...

How true!

[kenda47]

Checking Coupling Caps

Hi Kenda,

Thanks for your response. Coupling caps have not been changed. That was my first hunch BUT.. as I was having the same issue on both channels.. I assumed it was not the problem. I didn't think it likely that all coupling caps would need to be changed. A friend of mine who builds amps told me that its not common that the Blue Molded caps need to be changed and that it was best I leave them unless tested bad. What is the proper way to test for a bad coupling cap? As the amp is pretty much stock , I would hate to rip out all the coupling caps just for the sake of adding new ones, unless it is necessary. Thanks in advance for your response!

Greasy D'

Coupling caps are easy to test. They are connected between the plates of preamp tubes to the grid of the next preamp tube. Plates are pins 1 & 6 and grids are 2 & 7. Since you say it is both channels I would concentrate on the caps between the phase inverter to the power tubes. Basically the caps are there to allow signal to pass but block DC from the plates leaking through to the grid of the next stage. So you lift the ends not connected to pins 1 and 6, set your meter to read DC volts and measure to ground with the amp switched on in play mode but nothing plugged in. If you get any DC reading atall the cap is leaking and will trash your tone. If you want the amp to play the way Leo intended change the cap. As I said before this is an old girl. You can allways keep the originals in a bag and tape it inside the cabinet so if you ever sell it to a collector you can put the orinals back. It will probably sound crap again though.

[52 Bill]

Kenda47's description is perfect for finding leaky coupling caps, but that doesn't test for off value ones. The symptom of loss of low frequency response makes me look towards caps that have gone down in value. If it effects both channels check the cap at the input of the phase inverter and the post PI caps.

[kenda47]

Hi 52Bill. I realise that testing for leaking coupling caps doesn't confirm their value but I don't think it would matter what it's value had become if it is leaking it cannot do its job properly and I know the tone will suffer. This amp is an old girl and I would love to own her working or not. I have many old fender amps in my collection but not an original 65 Blackface Lux. I know I could get her working good as new. I have 6 65 Twin Reverbs all of which worked when I got them but they didn't perform until I restored them. These amps are now safely under lock and key which is a real shame because they all sound wonderful but there is no way I could gig with them as they would get stolen. I know this because i used to have 7.

[bohema79]

Hi,
Did you solve the problem?
I have a similiar issue with my vintage 1966 Fender Princeton Reverb.
Please let me know.
Cheers

[Raybob]

Hi,
Did you solve the problem?
I have a similiar issue with my vintage 1966 Fender Princeton Reverb.
Please let me know.
Cheers

Don't know if he did, but your cap can and bias cap fail from age, not use. Most likey, if your amp is 66, it needs a cap can and bias cap. Doe your cap can look original? If it does, REPLACE it, and order a 50@50 to replace your bias cap at same time.

[bohema79]

Don't know if he did, but your cap can and bias cap fail from age, not use. Most likey, if your amp is 66, it needs a cap can and bias cap. Doe your cap can look original? If it does, REPLACE it, and order a 50@50 to replace your bias cap at same time.

Hi.
The Can cap and all the electrolitics have been replaced.
The Can cap is a fresh CE 20/20/20/20
The bypass caps are Sprague 25/50
The bias cap is a Sprague 50/100

All tubes have been tested and work fine.