Harmony H415 problems, help!

[string bender]

Because of physical delaminating caps my recent purchase of a 1966 harmony H-415 amplifier with (2) 12'' jensen speakers I decided to change all caps and resistors recently.

My amplifier sounds "anemic" now, lacks volume on 3 out of 4 of its inputs, J1, J2, J3.
J4 is the mic input and with my guitar its a monster tone of loudness breaking up sound!

The amp is so low in volume on J1, 2 & 3 that my guitar volume cannot be heard until approaching 9 going to 10 on my guitar.
crazy.

any suggestions?
regards
Doug

[mresistor]

what caps and resistors did you replace ?    all of them?  Did you put C1 in backwards  ?  Lift one lead of C1 and test .


https://el34world.com/charts/Schematics/files/Harmony/Harmony_415.pdf

[sluckey]

How did it sound before you fixed it?

[string bender]

I changed R1,2,3,4,6,7,8,9,14,15,17,18, 19,20,21,22,23,24,25,26,27,28, 29, 30, 31,32, 33,34. (resistors).
I changed the electrolytic can type with a 40/20/20 500v and added a 50mf 100v which connects off of pin three (yellow wire) V3 & V4 to ground. The 130ohm 5w resistor is in parallel with the cap.
I replaced all the caps with the exception of the ceramic disc type of which (2) are connected to V1, (2) are connected to channel 1 volume/tone, (2) are connected to channel 2 volume/tone.

My amp sounded good when I first played it (60 minutes) I believe I stayed on the mic channel and played both a single coil and hum bucker. The channels J1, J2, J3 were sounding quite good but I liked the overdriven mic channel.
I hooked up a fender reverb tank to it and jammed out on the mic channel with my Heritage 535 (similar Gibson 335), it sounded like Hollywood Fat's tone, this knowing why he enjoyed it.

Because of a challenge and time on my hands (retired) I wanted to enhance the longevity of this classic amp. When I smelled heated plastic and then found the caps splitting I decided to change all the resistors/caps. Another blog member suggested too.

I carefully took lots of detailed pictures and drawings.
Made my list of items, got them in and installed.
I did not replace C1 nor did I replace R5, both are connected to V1 pin 7.
I have just removed both and tested.
Here are the findings; C1 = .97nf (isn't that equal to 970pf?)
                                 R5 = .44m (isn't that equal to 440k?)

[sluckey]

What voltages do you have on V1 pins 1, 2, 3, 6, 7, and 8.

[string bender]

correction: C1 = .27nf

readings for V1 pin 1 = 38v
                       pin 2 = -.6v
                       pin 3 = 0
                       pin 6 = 81v
                       pin 7 =  0v
                       pin 8 =.74v

[string bender]

V1 pin 1 voltages low.
Anemic sounding amp.

A friend mentioned possibly R27 drifted? Either side of R27 feeds V1. I will remove R27 and measure.

The following readings complete the assessment.

V2.  pin 1 = 168v
      pin  2 =      .7mv
      pin. 3 =    1.3 v
      pin. 6 = 253v
      pin  7 =     6v
      pin  8 =   19v

V3  pin 2 =       .27mv
      pin 3 =.   10.6v
      pin 7 = 300v
      pin 9 = 304v

V4. pin 2 =     .25mv
      pin 3 =   10.6v
      pin 9 = 304

V6 pins 2 and 8 = 306v

Electrolytic can
square = 271
triangle= 129
D =         305

Voltage on either side of R 27 is 129 and 271.

I do not know what to think, this is all difficult to understand, attempting to resolve this problem.
Thank you to those that are engaged in this post.

[nandrewjackson]

It makes sense that inputs one thru three are significantly less loud than input four. Inputs one and two have 68K parallel 390K to ground which will greatly attenuate passive guitar pickups. Input three Has 68K parallel 2.7M to ground, not much different than inputs one and two, although they go into a different triode. Input four has 2.7M to ground. BIG difference to inputs one thru three! However, considering all inputs have either C1 or C2 to ground, assuming they are 1000 pF, all inputs, to ground are now  30K  ohms at high frequencies, and about 1M at the low E string, to ground. These caps, combined with the resistance in parallel to ground at each input make for some big signal loss right at the front end.


It seems to me that you rebuilt the amp, and did a good job rebuilding it. Input 4 is the only logical choice for guitar, based on the schematic, and it's still a far cry from commonly used input stages.
IF IT WERE MY AMP, I would leave inputs 3 and four stock, and change inputs 1 and 2 to modern specs. Cut out C1, change R5 to 1M, and make either input one or two a non-switching jack. 
Then you could have the amps original sound in low (input 3) and high (input 4). And have a "modern" input in input one or two. Whichever one is the switching jack.

[string bender]

Thank you to those helping me with this amplifier.
I admit It took me some time to remember how to correctly solder. I may have overheated some components.
I have checked and checked many times of my drawings, my pictures, other peoples pictures and a video online that I could freeze frame and check my wiring.

R27 seemed to be the culprit not allowing the first stage come alive.
Anemic sounding amp vs what I've heard other H 415's sound on video and its approaching the volume I had before I yanked out the caps/resistors.
I just changed R27 from 100K to 77K (was an older resistor I reused, 68K now 77K measured).

Here is the results of before and after on voltages and then compare to what the schematic calls out.

Before with 100K               After with 77K                            Schematic
V1 pin 1 = 38                             42                                          68
     pin 6 = 81                             92                                        100
V2 pin 1 = 168                           165                                       190
     pin 6 = 253                           251                                       260
all other numbers same as presented with the exception of the electrolytic can
triangle was 129                   now 149                               schematic 150
square  was 271                   now 271                               schematic 280
D          was 305                   now 306                               schematic 310
...
guitar levels checked per my ear.
Conclusion: its louder on J1 - J2 -J3. Still seems not much volume and the way this amplifier reacts to your guitar volume potentiometer is the strangest. It still doesn't give me any sound until Passing approximately 9 going to 10.
When plugging into J4 or the Mic jack it is approaching acceptable volume levels per my ear. I thought an 18 watt amplifier would be louder.
Its important to recognize that the sensitivity that exists in J4 (mic), my volume pot volume comes on much earlier but still nothing until you get say around 4 or 5. Also the pot is scratchy on the guitar...not on any other amps by the way. Also the pickup selector when changing pickups and the Strat  5 way switch makes very loud noise every time you change pickups.

I also had difficulty measuring pin 7 on V4? Strange, almost like the solder was not conductive?
I heated the pin up and moved the solder around. After it cooled it acted the same, very difficult to get a DMM reading.

nandrewjackson I have read about some suggestions for this amp to change out the inputs. I purchased two switchcraft, self grounding type however I do not have 1M resistors yet. Also I am not understanding your suggestion fully. Can you help me understand. You mention removing C1, change R5 to 1M resistor, but you mention make either input one or two a non-switching jack?
Is this the standard Fender set up?

Discussion: Question? is there a way to check the transformers? Possibly I have a change in resistance vs a new one? How would I check such a device.

How does this EL 84 tube amp differ from a Marshall 18 blues breaker type amp?

What amplifiers could and would be practical to change to? ( consider using cabinet, chassis, components for basic platform).

Thanks.

[nandrewjackson]

this drawing shows the equivalent of what's happening when you plug into any of the inputs, assuming you only plug into one at a time.  As you can see, inputs one thru three give very low resistance to ground, in addition to the 1000pF in parallel, which lowers the resistance even further, which is sending a lot of the guitar signal to ground before it even gets to the tube grid.


input four has the highest resistance to ground, but it still has the 1000pF cap which drops that 2M resistor down to a maximum of about 30K ohms to ground for high frequencies and 1M for low guitar frequencies, to ground.  Which is still considered very low resistance to ground for the input stage of a 12**7 input grid.


The fifth example shows a "modern" (lets call it that for simplicity) 12**7 input bias.  68K in series and 1M to ground.

[nandrewjackson]

this drawing shows what would happen if you cut out C1 and change input 2 to a non-switching jack.


input one would be the loudest input of the amp.  Input 2 would be very close to stock.  Inputs 3 and 4 would remain stock.  Leaving R5 390K would still make input 1 louder than input 4 is currently.

[string bender]

Installed non switching input jack. (not sure if its the correct style/part). When removing old input jack I had to remove ground to J4.
Upon initial power up channel 2 was noisy, I installed a ground for J4 and this quietened the noise.
It appears plate voltages on V3 and V4 are oscillating about 6 vdc. Pin 7 on V4 is unreadable. (is it safe to read pin 7?) How do you test a power transformer?
J1 tone and volume are spot on.
J4 tone and volume similar to J1 but I think J1 tone is better.

[shooter]

V3 and V4 are oscillating about 6 vdc

turn off the tremolo and that should stop

is it safe to read pin 7

with NO signal, and a meter that can handle the VDC, typically is not a problem.

You can ohm it also and compare V3 p7 with V4 p7
make sure power is OFF, caps bleed down, amp Unplugged.
pull both PA tubes, unsolder the CT lead at the filter cap, then clip a meter lead to the wire.
stick the other lead in the tube socket, tube side, record value, repeat for other socket, they should be reasonably close

[string bender]

shooter: yep thanks for noticing I had the tremolo on...dummy me.

in regards to the transformer:
Greenwire or V3 pin 7 = 168ohms
Brownwire or V4 pin 7 = 148 ohms

??????

I don't have spec's on that yet. How does it look to you?
To me it seems suspect?

[shooter]

pin 7 = 300v

that seems within acceptable, so;

V3 pin 7 = 168ohms

also, possibly acceptable, based on the 300vdc

so I would re-measure your Plates, swap tube and repeat

to keep things safe, gator clip your meter leads instead of trying to stab 300vdc n missing

[string bender]

I removed pin 7 from V4 and inspected and cleaned it, I swapped it for pin 1 which isn't used, cleaned both, they had some dark gunk on the surface so I used throttle body cleaner (auto) and it removed the gunk immediately. Took a jewelers file to the pins and cleaned the terminal and pin area. Resoldered. New power tubes installed (matched sovtek).
I was able to read pin 7 but it makes some strange sounds and first attempt was unsuccessful. I have to hold my lead right at the tip of the pin vs on the wire.
Measures 306

here are my last readings.

V6 pin 8 = 310

electrolytic can

D = 311
Square = 273
Triangle = 151

R27 resistor values on either side (77K ohm in place of 100K) is 151/273

V1 pin 6 = 95
     pin 1 = 44?
     pin 7 = mv or 0
     pin 8 = .82

V2 pin 1 =173
     pin 3 =   1.3
     pin 6 = 253
     pin 7 = 6
     pin 8 =  19

V3 pin 3 = 10.3
     pin 7 = 304
     pin 9 = 308

V4 pin 3 = 10.26
    pin  7 = 306
    pin 9 = 306

[sluckey]

That schematic has an error. V1 pin 3 should not tie directly to ground. There should be 1.5K resistor between pin 3 and ground.

Or... there should be a .022µF cap between the junction of R3 and R4 and the junction of R7, C2,  and V1 pin 2.

[string bender]

My amp wiring has been the following.

V1 pin 3 connects to pin 9 and from there ''two connections". (1) to tube socket ground. (2) jumper to V2.

V1 pin 2 connects three places (1) hard wire to a terminal lug that connects a resistor to input jack. (2) 1.5k resistor to ground lug of terminal strip and in parallel with a (3) ceramic disc cap.

Sluckey? Should I remove the ground attachment from Pin 9 on V1?

[sluckey]

I'm not suggesting you change anything. Just pointing out that the schematic appears to have an error. The schematic shows 0v on the grid and ground (0v) on the cathode. That's bad! This tube should be operated with a negative voltage as measured between grid and cathode. But the schematic shows zero. That would explain your very low plate voltage if the amp is actually wired like the schematic.

[John]

I opened mine up again and took a few pics. Pin 3 is indeed grounded, over to pin 9 which is grounded to a tie point. This is factory I believe. Not my doing for sure. I assume they are using some sort of clever voltage bias thing I've read about ?

[sluckey]

John, can you verify that in your amp pin 2 is wired IAW the schematic posted above?

[DummyLoad]

sluckey - i also had a harmony H415 and pin 3 was grounded as per schematic - i modified the one i had to use cathode bias. pin 9 of V1 is also grounded as per the schematic. there was no input cap on pin 2 of V1. the one i had was unmolested internally but it came to me with celestion alnico blue speakers. i kept the speakers and sold the amp. the new owner converted V1 section back to grid-leak bias.


--pete

[John]

John, can you verify that in your amp pin 2 is wired IAW the schematic posted above?

Will do, I'll take a pic from a different angle. But yes, the mica cap is going from 2 to grd, as schem shows. I was going to take voltages last night, and more pictures but ran out of steam.

[string bender]

Here is the latest pics of replacing resistors/capacitors. I replaced J2 with a non switchable input and and J1 is as loud as J4 (mic). J2 and J3 are anemic (low volume no breakup).
again whats strange about this amp presently is guitar volume is not responsive until volume passes 9 going to 10 on J2 and J3. Guitar volume is not responsive until volume passes 3 on J1 and J4.

[string bender]

more pics

[string bender]

more pics
includes 50mf 100v electrolytic

[sluckey]

My amplifier sounds "anemic" now, lacks volume on 3 out of 4 of its inputs, J1, J2, J3.
J4 is the mic input and with my guitar its a monster tone of loudness breaking up sound!

According to the schematic, this is how those input jacks should work. J3 and J4 are wired as a typical HIGH-LOW pair. J4 is the high input and J3 is the low input. J1 and J2 are wired as both being LOW inputs (sounds stupid but it is what it is). So, J4 is the only high input.

Here is the latest pics of replacing resistors/capacitors. I replaced J2 with a non switchable input and and J1 is as loud as J4 (mic). J2 and J3 are anemic (low volume no breakup).
again whats strange about this amp presently is guitar volume is not responsive until volume passes 9 going to 10 on J2 and J3. Guitar volume is not responsive until volume passes 3 on J1 and J4.

This is how the jacks should behave after you replaced J2 with a non switching jack. You basically converted the J1/J2 pair to a HIGH-LOW pair, with J1 being the high input.

[string bender]

Sluckey,
Have you ever experienced a guitar volume pot that only is effective from 9 to 10? It is silent below 9 on J2 and J3.
Because I changed out J2 to a non switchable jack, J1 and J4 are now silent below 3 on the volume of the guitar.

I find this rather strange.

I welcome folks to view my pics and look at the schematic.

I await John's pictures, that way I can compare the two.
Of course If I were of greater knowledge in amp troubleshooting/maintenance I would be good at following the schematic, however I am a new at this. I very much appreciate the help and concern in this matter.
Kind regards
Doug

[sluckey]

Lot's of different interactions can occur when plugging a guitar into any amp. Pickups and tone/volume pots in the guitar are a factor the same as the amp input circuit. Really need to see a schematic of your guitar and pickup specs to give a specific answer to why you have silence before a certain number on the dial. I would not fret over the differences in the input jack operations. Just plug into a HIGH input and play loudly. You only need one input. 

Read page 8 of this pdf for an explanation of hi/low input jacks...

     http://sluckeyamps.com/misc/Amp_Scrapbook.pdf

Also, keep in mind that Harmony was a bottom feeder name in amps/guitars. You could buy them at Woolworth's or Western Auto, but rarely in a music store that sold Fender, Gibson, Ampeg, etc. Don't expect too much.

John's amp and DummyLoad's amp are both wired just like yours as far as the input wiring is concerned. I don't know why there is no cap between J3/J4 and V1 pin 2. That cap is an important part of the operation of a grid leak bias circuit. The amp is built IAW the schematic. I still think the engineers accidentally omitted that cap, but the amp obviously works as is. And when dealing with a $40 amp, there's not gonna be much QA inspection. Not the first time there have been engineering quirks. I've seen some in high end name brands too.

[John]

Okay, voltages. Quite a bit higher than OP, maybe due to my normal 127 vac at the outlet? Anyway...
V1
1-77
2-0
3-0
6-150
7-0
8-1.1


V2
1-235
2-0
3-1.6
6-342
7-8


EL84s:
2-0
3-15.7
7-412
9-409


C11-415
C12-365
C13-202


They be hot,but it get's played 1 hour per year. I think it'll last. 

[John]

since I have it opened up, I'm going to re-do the filter caps. They're not attached like they should be; when doing this (my first "repair") I was not yet fully aware of Good Practice. Probably replace the rest of those CC power resistors too. They smell funny. ;) Maybe re-route the heater wires?


Amazingly, everything works including trem, and the amp sounds great. I chuckled at how tiny the transformers look though, for an "18 watt".


SB, if you need more pics throughout I'm happy to take more.

[shooter]

Amazingly, everything works including trem

That's always been my "cue", I moved on to the next problem 

IF you do dive in, plan well, do 1 thing and verify, take lots of pics, in the ol days I'd sketch alot 

[John]

Well this has been "re-done" by me quite a few years ago. My first project. I'm looking at some of those joints, and lack of support for filter caps, and just can't let it be. lol


But after thinking, I'm not touching the heater wires. It doesn't have any nasty hum at all. Probably due to the undersized OT can't handle anything below 80Hz. 

[sluckey]

If this were my amp... I'd remove that jumper between pins 3 and 9 on V1. I would install a 1.5K resistor between pin 3 and chassis ground using the same ground point that the 1.5K connected to pin 8 is using. Then replace that 2.7M resistor on pin 2 with a 390K. This will make both channels exactly the same.

Finally wire each pair of input jacks as a typical HIGH/LOW arrangement.

[John]

I'd remove that jumper between pins 3 and 9 on V1

I was thinking of doing that on mine. But gosh, I'd hate to mess with the mojo. 

[John]

So, I followed Sluckey's suggestion and put the 1.5k cathode resistor in. It sounded good, but since I couldn't A/B it can't say it sounded better. However brought up the voltages for that side as expected. I then clipped on a 10uf cap, and oh my Heavens. Really put some bark in it! Highly recommend that. Then again, after I play it for another hour I might change my mind.


Pics of the PT section are for SB's comparison. Pic of the filter cap section is just to show how I did it. I added a couple lug strips. Replaced the 1W CC power resistors. Upped the screen R to 1K .


I really like how the amp sounds, it's not as "sterile" sounding due I supposed to adding the cathode cap on V1.

[John]

I'm going to change out the jacks for switchcrafts too while it's apart.

[string bender]

John
thanks for posting pictures!
Doug

[John]

SB, notice that I took out the cap can completely. Now all the filter caps are axials. That's because that's the style I have. You could use the radial type too. I forget if you already did anything with the filter caps. If not, that's probably your main problem. Maybe.


Mine is PLENTY loud, always has been, really on any jack. J4 is noticeably louder, but even the others while quieter and maybe not as "rich" sounding still give plenty of volume.


IMO, replace your filter caps and your voltages will probably be higher throughout than what the schematic calls for.


I've been busy with work, so haven't been following everything as closely as I usually do.

[string bender]

John

I replaced all the caps, including the electrolytic caps.
I found a can type 40/20/20 and installed a 50mf at 100v (thats the one with the xircon resistor in parallel).

I changed some things since last we spoke.

R27 changed back to a 100ohm resistor (was 77), xircon resistor was supposed to be 130ohm at 5 watts but it drifted to 122 ohms, I put the replacement in 150 ohms (cause you can't find the 130's). I chose to do this
because the amp was too overdriven on J1 and J4.

Something happened ???? and its got some noise in it.
The following are the last voltage readings.

V1 pin 1 is 43
     pin 6 is 93
V2
pin 1 is 193
pin 6 us 296
V3
pin 7 is 353 (this is high, supposed to be 310)
pin 9 is 358 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
V4
pin 7 is 354 (this is high supposed to be 310)
pin 9 is 358 """"""""""""""""""""""""""""""""""""""

on the electrolytic can
the square is 318
the letter D is 360
the triangle is 150

V5 pin 5 is 184 -220 (this is supposed to be 160)
pin 6 is 56

V6 pin 2 is 360 (this is supposed to be 320).

The amp was quiet before I changed the above components out.
I need to resurrect that.

[John]

Check that the ground lug on your new cap can is well grounded, as in zero ohms between it and the chassis. Look at the joint in hi rez. A hairline crack, or "cold" joint will be just enough to cause you problems.

[John]

Hey, I'm looking at your cap can. How exactly is it grounded to chassis?

[string bender]

John

the tangs of the can are soldered to the chassis.
Also a grounding lug attached with an aircraft bolt, washer, self locking nut (3/16th'').

Did you notice the 50mf electrolytic cap? The 5w 130ohm resistor in parallel with it?

I was fortunent to have an amp repair guru walk me through that set up along with the three prong
Cord connections which my standby switch is disconnected.

[John]

Voltages after installing cathode resistor on V1-3



V1 1-135
2-0
3-forgot to measure, but now has 1.5k||10uf to ground
6-165
7-0
8-1.1 - has 2.2k cathode resistor. I must have not had 1.5k at the time. Leaving it, sounds fine.
 V2
1-235
2-0
3-1.6
6-342
7-8
EL84s:
 2-0
3-15.7
7-412
9-395 -changed the screen R to 1K from 560 ohm
C11-415
C12-365
C13-202


Measure your wall voltage. It's probably around 120 AC. Mine is usually 123-127. Something is mis wired if you're getting normal/slightly high readings at  the filter caps (your can) and yet very low voltage at the first preamp tube. That's probably why your J1-3 is so much quieter than J4. Like I said before, mine are slightly quieter, but not that much.


Remember to have all knobs turned to ZERO when taking voltages. Especially your tremolo knobs.


And you have tried a new tube in V1? Should be a 12AX7, available at any self respecting music store. Again, the voltages at your power tubes look just fine. Higher than schematic which is totally normal. Your V1 voltages should not be low unless something is wired wrong, or you have a wrong-value resistor somewhere. (Easy, easy mistake to make)


Your voltages across R27 seem right, you're drawing about 1.5mA (voltage drop / R value = current .0015) Figures on schematic show 1.3mA, I'm dropping about 1.6mA on mine. SO, the V1 is getting rid of voltage somewhere.

[string bender]

John
I have changed V1 12ax7.
I just checked R8 and R9, those are both 100K resistors.

Would changing either help me help in this matter.

I cannot find any issues with my wiring. I've gone over and over and over it.

Doug

[John]

I just checked R8 and R9, those are both 100K resistors.Would changing either help me help in this matter.

Only if they're way-way out of spec. Anything between 80K and 120K should still be "close enough".


Measure resistance between pin 8 and ground. If that is around 1.5k ohms, then take a close look at your volume & tone pot wiring. Make sure no leads are touching or close-to touching.


If you can't find anything there, try disconnecting C4 & C6 from their ground point. Then take voltages on V1 again, with all pots to zero.


I am about 1% as good as most guys on here at trouble shooting. This is just the stuff I'd be trying if it was on my bench.

[string bender]

I need some help from Senior people.
Sluckey, others.

I measured resistance from input center pin to V1 pin 2, pin 7.
The reasons are the following.
J4 is similar in volume to my modified as outlined in this blog to J1 however J4 is of tonal quality/volume "too hot" but what is most important is that J4 is "unacceptable" because THE GUITAR VOLUME KNOB IS SCRATCHY LOUD WHEN MANIPULATED UP OR DOWN.

I have complained about this phenonmenom and possibly the reason for lack of diagnose is my lack of providing information so I am attempting to provide such.

input                            Sound                  V1 pin 2                    V1 pin 7
J1                                a bit too loud         433 ohms                  68 ohms
J2                                anemic                  170 ohms                  68 ohms
J3                                anemic                  68 ohms                    203 ohms
J4         scratchy volume/too loud               34 ohms                    2.7M ohms

...................................................................
John V1 pin 8 is 1.5K ohms             

[sluckey]

If this were my amp... I'd remove that jumper between pins 3 and 9 on V1. I would install a 1.5K resistor between pin 3 and chassis ground using the same ground point that the 1.5K connected to pin 8 is using. Then replace that 2.7M resistor on pin 2 with a 390K. This will make both channels exactly the same.

Finally wire each pair of input jacks as a typical HIGH/LOW arrangement.

[string bender]

Thanks Sluckey.

I've got your reference and ordering parts today.

Merry Christmas

[string bender]

Looking at the schematic, C1 and C2 show a value of 100

I do not know if its nf or uf, nano farads or micro farads.
I am concerned because the ceramic disk C1 measures on my multi meter = .97nf and printed onto the disk is "100". 

Other Capacitors in the circuit like the common .022 is uf or micro farads.

Its difficult for me to believe C1 and C2 are measured in Micro Farads.

I am confused.
HELP!