Airline 8504 restoration now underway.

[1blueheron]

Anyone have any information on this Airline? Google not returning much.  Was it made by Valco or Danelectro?  Model seems to be missing from the schematic library.

Here is a pic of the model number.   Chassis and tubes looks like they are all there. Cabinet is very rough and the speaker cone has some tears.  Grill and grill cloth seems ok.    Worthy of time, $ and effort to restore?  Good candidate to learn basics of repair and restoration on?

[1blueheron]

grill

[sluckey]

Maybe this...

[munkeyboy]

The circuit looks very much like the silvertone 1472/1482 circuit.  The inputs, the rectifier and power look different, but everything else looks similar.  I'm guessing that is Danelectro made.  Maybe a 10 watt amp instead of 15 watt.

[Willabe]

Can you post a clear pic of the tube chart on the amp cab wall?

[1blueheron]

Maybe this...

Thanks Sluckey,  Not sure of the significance of the "a" designation in addition to 8405 but I think it is probably the correct schema.  Since the amp is not in my hands I cannot yet confirm.

Can you post a clear pic of the tube chart on the amp cab wall?

Here is a pic and clarification of the tube chart on the amp wall. 

[munkeyboy]

FYI, there is one more 12ax7 i believe in the upper control panel not shown in that tube layout.

[DummyLoad]

that's the same tube lineup in the schematic that slucky linked to.


--pete

[1blueheron]

FYI, there is one more 12ax7 i believe in the upper control panel not shown in that tube layout.

Correct.  It is in the trem/control upper chassis unit.

that's the same tube lineup in the schematic that slucky linked to.

  --pete

Yes, I believe Slucky has given me the correct schematic, just not sure if there is a subtle difference in the "a" designation.

[munkeyboy]

Not the same amp, but the silvertone 1344 and 1344a are the same amp except the "1344a" had a speed control and an intensity control for the tremolo/vibrato. the "1344", just had intensity.   Could be something like that.

[1blueheron]

Further investigation says no real difference between the "a" and non a versions. 

I closed the deal on the airline and should be picking it up next Sat.  Planning a full resto.

Found a Youtube on resto of the 8503.

Also found it is pretty much identical in circuitry to the Danelectro Centurions.

[1blueheron]

Picked up the Airline 8504 and brought it home yesterday.  Took it apart today for a thorough cleaning and assessment.

The chassis' both cleaned up nice.

I am not sure the speaker is original to the amp.  It is a 15"  speaker EIA numbers 328001 fix it as a Utah.  Was able to patch the damaged areas in the cone and it appears it will be serviceable.  Cutout in the baffle is smaller than 15" but there are no unused mounting holes.  Strange and puzzling.  Anyone know for sure what size/make speaker was stock in the Airline 8504?

The tolex is pretty worn and the back panel is missing.  It was replaced with a homemade panel which was installed lower in the back of the amp.  I am guessing this was to accommodate the 15" speaker of which the magnet extends back slightly too far for the original back panel to work.  Planning a workaround for this.

I need to replace the 2 wire power cord, then plan to do voltage checks and see what i've got.

The 6V6 tubes are not matched up.  One is a Sylvania, the other is an RCA.  Sylvania has a halo and they have different plate styles and lengths.  I am guessing they should be replaced with a matched set?  Will post pictures up shortly of the progress.

[PRR]

> a matched set?

Why?

It will play fine, unless tubes are outright sick.

[1blueheron]

> a matched set?

Why?

It will play fine, unless tubes are outright sick.

Well,  I just thought it would probably sound better if the pushing and pulling was equal, I'm sure it will work as it is but maybe not sound its best?

[1blueheron]

Here's some before and after the cleanup.

[1blueheron]

More pics..

[1blueheron]

Hoping to get the power cord replaced and the "death cap" removed today.

[1blueheron]

New 3 prong power cord installed.

Removed c14.

Plugged it in and powered it on to do voltage check but started getting smoke from c9,10,11 bundle so I shut it down.

It appears C13 has already been replaced as it is now a 20MFD rather than the 16MFD on the schematic.  It looks like it is new as do C12A and C12B. 

Can anyone tell me where C6 is?  Not seeing it.

Looks like I will be ordering parts.

[sluckey]

C6...

[1blueheron]

Thank you Sluckey. 

[1blueheron]

All of those Sangamo Type 33 caps are labelled as 600V.  If replacing is it necessary to use 600V or is 400V sufficient?  I don't see any points where voltages over 400 would be encountered. Am I looking at this wrong?

 

[sluckey]

I would use Mallory 150s or Xicons for replacements. Both are small and rated for 630V.

[1blueheron]

Thanks Sluckey.  I had those Mallory 150's in the shopping cart when I posted but seeing Doug is closed until next week and I was wondering if something else in my scavenged parts bin would suffice for testing until I could get proper long term replacements.

Do all the caps in the amp need to be +600V rated (such as C15,16,17,18) or can these be of lesser voltage?  I tried Google on this and it seems the opinions vary.  Some contend unloaded rail voltages can be high before load is applied or when testing with some tubes removed, while others say 400V in the preamp section is adequate and may be fine other places depending on rail voltage. Also arguments about continuous use vs. short term tranisents etc.

In my case, the power supply filter caps are rated at 450V and the highest rail voltage listed is 280V which makes me wonder if OEM 600v was overkill.

I have some 400V Blue Molded caps in proper values on hand and I also have some 6PS 600V Orange Drop caps and Aerovox Brown Dip 600V caps

Is it inadvisable to use  2x  .047uf 400V Blue molded caps in series to replace the .02uf 600V caps (C9,10,11)? That would give me .023uf at 800V correct?  Or similar combinations of series/ parallel with the 600V orange drops/brown dips to get proper values for other caps?

[1blueheron]

Found another close relative...

https://www.vintageguitar.com/22134/danelectro-viscount/

[DummyLoad]

400V coupling caps will work - worst case is 375-ish volts on cold startup startup for a few seconds.


--pete

[1blueheron]

Thanks Pete!  That means I can probably get it up and running for voltage checks today!
 

[1blueheron]

I postponed voltage checks and re-power due to some concerns about the 6X5.

Here are my concerns:

I have very high mains voltage here.  We are typically 125V.  From using that dangerous tool called Google, I ran into a mess of posts about how the 6X5 has issues with modern day line voltages.  Many recommend replacing it with diodes, converting it to 6X4 or converting to an EZ81.

Is there anything here to be concerned about or is this all just a tempest in a teapot.

My old Eico tone generator suffered a 6X5 failure when I plugged it in. Probably caused by a faulty cap but it blew the 6X5 on power up.  Perhaps this makes me over sensitive to this issue.

I Have plenty of empty octal bases I can make a ss replacement with if that is the better/safer way to go without making radical modifications.   I realize it will change the sound but since we don't know what it sounds like yet, I'll never know the difference..

[shooter]

We are typically 125V

The datasheet I looked at says 325Vac cap, or 425vac choke, rms per plate so that is your starting to guess point

[terminalgs]

re 6X5GT.  There was a recent thread about 6X5/6X4's -->  http://el34world.com/Forum/index.php?topic=23673.0


I have an airline with a 6x4. I put some 1N4007's in series with the 6x4 and decided not worry about it anymore.   (in series between PT and tube, using unused pin lugs on the sockets --if you have unused lugs ., it looks like danelectro used a few on that octal...)


that is a certainly a danelectro build.  notice the "GDR" in the GDR8504 was the montgomery ward identifier they stuck in item#'s to identify the manufacturer.  GVC was valco.  as for the "A" suffix, that is just a catalog pn# suffix number.  I'm not exactly sure how MW decided on the suffix,  but the "A" wasn't anything to do with an engineering version (like a 12AX7A, or a 6L6A..) and it wasn't specific to amplifiers.  The guitars has that suffix as well.  Sometimes the catalog pn# suffix would be different if it was a bundled set., like a guitar might be a 7092A and the case is a 7766A but the bundled guitar and case was 7093AA ?!!?  also, for amps,  sometimes the catalog pn# would be a "R" or "RTT" for amp + cabs, and there are some combo amps with a "RD" or a "B" suffix (no bundling needed for a combo).  "62" is something you see a lot with MW amps and guitars.,  "62" was the department number.

[1blueheron]

We are typically 125V

The datasheet I looked at says 325Vac cap, or 425vac choke, rms per plate so that is your starting to guess point

Shooter,

Thanks, So I have a cap filter input amp if I am not mistaken.

The schematic references line voltage at 117Vac, and shows rectifier plate voltage as 260Vac.  I assume pulling the tubes and checking voltage at pins 3&5 will tell me if I am within the 325  design limit while running it at 125Vac line current, and I assume I will will probably be in the 280-290V range at pins 3&5.

Does this mean I am in the clear and have no reason for concern?  My thinking is that if I replace the caps and check all the resistors and everything is good, it should work fine for another 60 years... 

re 6X5GT.  There was a recent thread about 6X5/6X4's -->  http://el34world.com/Forum/index.php?topic=23673.0


I have an airline with a 6x4. I put some 1N4007's in series with the 6x4 and decided not worry about it anymore.   (in series between PT and tube, using unused pin lugs on the sockets --if you have unused lugs ., it looks like danelectro used a few on that octal...)


that is a certainly a danelectro build.  notice the "GDR" in the GDR8504 was the montgomery ward identifier they stuck in item#'s to identify the manufacturer.  GVC was valco.  as for the "A" suffix, that is just a catalog pn# suffix number.  I'm not exactly sure how MW decided on the suffix,  but the "A" wasn't anything to do with an engineering version (like a 12AX7A, or a 6L6A..) and it wasn't specific to amplifiers.  The guitars has that suffix as well.  Sometimes the catalog pn# suffix would be different if it was a bundled set., like a guitar might be a 7092A and the case is a 7766A but the bundled guitar and case was 7093AA ?!!?  also, for amps,  sometimes the catalog pn# would be a "R" or "RTT" for amp + cabs, and there are some combo amps with a "RD" or a "B" suffix (no bundling needed for a combo).  "62" is something you see a lot with MW amps and guitars.,  "62" was the department number.

Terminalgs,

Thanks for confirming the model/letter designation and history bit.  I got the amp from my BIL.  He has an Airline Bobkat guitar that he thinks came with it.  Is it possible the "A" was a designation that it was part of a Guitar/amp starter kit in the catalog and sold together?  This might explain a few things.  I can confirm that everything is accurate on the schematic Sluckey posted. 

The diodes you mentioned as having placed in series with the 6X4, they serve just as a safety measure but have no effect as long as the tube is functioning correct?

I ran across mention that it might be possible to use a 0Z4 or 0Z4G as substitute for a 6X5.  Full wave rectifier, octal base, similar specs.  However it needs 300V to fire up.  Not sure if this is correct but might be an interesting solution

[shooter]

unloaded will give you kinda sorta, the real test is loaded at Time 0 
you should be fine, for another 60yrs......optimism is a good thing 

[PRR]

> 0Z4 ....it needs 300V to fire up.

NO, that is a maximum it should ever see!!

It conducts at 24V.

It really is not suited for more than 250V car radio application.

Even then, it was rarely used--- maybe a clue?

My suspicion is that WHEN it shorted, it took-out the rest of the power supply with it. A vacuum rectifier has some limiting resistance.

6X5 is not unreliable. Don't let bad experience spook you.

[1blueheron]

OK, moving on.  Removed tubes and checked PT voltage last night.

Voltage at wall= 124.9V
Voltage to chassis ground at pins 3&5= 291V
Voltage to heaters 6.9V



In other business, replaced the 4 Sangamo caps in the preamp section.    In the process found a connection that appears to have never been soldered before it left the factory. Just stuck in the terminal loose. WOW!  Things were not very neat up there. I think they went to above and beyond to reduce component numbers in this amp    Some really rough looking solder joints.  Re-flowed all of those and inspected.


Checked resistor values in the preamp section.  Most of them have drifted upward a bit.  Ie. 68k are reading in the mid to upper 70's but I guess that is normal.  Will leave them as is for now.

[davidwpack]

10% would be about 74k. That's within the tolerance. I wouldn't worry about it.

[1blueheron]

Limited time to fiddle last night but did find that the two 68ohm resistors on the FIL side of the PT are considerably off reading 45ohms.  Planning to replace those.  Also found many of the 330k resistors are outside the +/- 10% range.  Worst was R18 2.2K which was toasted swollen, and reading .84K.   I replaced it.

Also replaced the .05 sangamo at C8 with a .056 orange drop 6PS

The person who replaced the Filter caps previous to me snipped the originals and soldered the new ends to the old ends and it looked pretty crappy so I removed and soldered that to the lugs properly.

Pretty much at the end of my rope until parts come now.

[1blueheron]

Got a few minutes last night to spend on the amp and as luck would have it when I got home, most of my caps had arrived as well as my new weller soldering station.  Woo Hoo.


I have 2 caps left to replace that have not yet arrived.    Resistors should arrive before the end of the week.

Now has a F&T 16MFD 475v for C13
C3 is 10uf 50V Illinois
c15&c16 are 400V Goodall.  May change later to experiment with sound.
c17&18 are 600V brown drops (might play with these as well)
c8 600V Orange drop 6PS series.
Remainder are Mallory 150's

The 2- 10uf caps will be replaced with Nichicon VX series 10uf 450V when they arrive.

Here is what it looked like after I finished last night.

[sluckey]

Neat work.

[1blueheron]

Neat work.

Thanks Sluckey.

[davidwpack]

Yeah. My first couple of amps looked like I shoveled the parts in there. Very nice work!

[1blueheron]

Is this indicating the voltage at this node should be 450V or is it indicating the voltage rating of the 16uf cap? 

[davidwpack]

I would say the latter? Could be wrong.

[shooter]

Cap, node vdc is 280

[1blueheron]

Cap, node vdc is 280

Thanks for confirming.  That's what I thought but it is strange no other cap values are listed other than C3 which is pretty obvious, so I wanted to be sure I hadn't missed something.

Also, just to confirm, the Mallory 150 caps are non-polar correct?   Everything I read says they are NP but there are lots of dissenting opinions on inner/outer foil and noise.  Any truth there or just noise?   

[shooter]

read n decide, also, in the achieve section is a thread, "do caps sound different"

the mallorys are NP

http://el34world.com/Forum/index.php?topic=11427.0

[1blueheron]

read n decide, also, in the achieve section is a thread, "do caps sound different"

the mallorys are NP

http://el34world.com/Forum/index.php?topic=11427.0

Thanks for that... Now I have to add checking polarity on all the caps to my todo list....

Well,  all the parts have arrived and are now installed!  Woo Hoo!

We have been running on generator power here for two days so voltage has been too sketchy to do much testing but it was fine to run a soldering iron.


After all the cap and resistor work was done, I put in all the tubes minus the rectifier and checked to see if all the heaters lit. They did,  Then I put in the rectifier and plugged in the guitar.  Man is this amp quiet!  Too quiet.  Absolutely no audio output, not even hiss or hum coming from the speaker. 

 Will try to do a full voltage check tomorrow night and post findings.

[1blueheron]

The problem was a pretty simple fix.  I found it tonight while attempting voltage checks.  I couldn;t get a reading on voltage between ground and any of the pins....  Then I realized when I installed the 16MFD F&T cap, I moved the CT and cap over one terminal to make them line up better.  The terminal they used to be on was the grounded terminal, so I had removed the ground for the CT.   installed a jumper and bingo, it is now alive and kickin'.   

How it sounds:

It sounds really nice but doesn't have much sparkle.  Perhaps its the 15" speaker in it.  Can't help but think it is rolling off some of the highs.  The trem works nice.

Things I still need to do:

Channel 2 is dead for some reason.  Need to get that sorted out.
Try it with a 12" speaker that will fit with back cover on
Recover the  cab and do some remaining cosmetic work
Install some rubber feet.

On the second channel issue, what would be required to wire the second channel (other side of the 12AX7) as a preamp boost or overdrive channel?  We really have no need for six inputs on 2 channels.  Seems like it might be a pretty simple and reversible mod that would make the amp a bit more versatile.  Also thinking of using slightly different resistor values for each of the 3 input jacks rather than them being all the same. 

[sluckey]

Channel A and Channel B are identical and very simple. Just compare voltages and resistance values (and caps too) between the two channels. Should be a quick and easy fix. Once you have both channels working try this simple cascade mod. Should give you quite a boost. But fix the dead channel first.

[1blueheron]

Thanks Sluckey, have I ever told you your awesome! 

Will keep you posted on outcome.

[sluckey]

Can you post some hi-rez pics of the preamp chassis?

[1blueheron]

Didn't end up with much time last night but did find the problem with ch 2.   and took some photos.

When looking at schematic and photos this AM, I realized I am probably referring to Channel A on schematic as Channel 2, and Channel B on schematic as Channel 1 (backwards).  I have always been called backwards, I guess this confirms it.  Anyway, I labelled all the photos to match what I am calling channel 1 and channel 2.    For clarity, my channel 1 connects to pins 1,2, 3 on the 12AX7 and channel 2 connects to pins 6,7,8.  which to me is logical.