Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Feb Sat 22, 2020 8:42 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 131 posts ]  Go to page Previous  1 ... 3, 4, 5, 6, 7  Next
Author Message
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Sun 15, 2017 2:38 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14047
You can use either metal or glass but AFAIK the 6888 was only mfg'd in glass... It's all I've seen and nothing in the tube registrations suggest there were metal versions...

Tom


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Sun 15, 2017 3:16 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
35Z5 wrote:
You can use either metal or glass but AFAIK the 6888 was only mfg'd in glass... It's all I've seen and nothing in the tube registrations suggest there were metal versions...

Tom



Your right. I was looking at so many tubes last night it all became a blur. The 6SQ7 seems more plentiful in metal. Still trying to find the last few parts. Can't seem to locate a source for the referenced trimmer cap (C5) Digi-Key had some but had to buy in bulk =$. Also looking for cap C9 with the correct spacing. The board looks tight so not sure how much wiggle room there will be.


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Sun 15, 2017 10:45 pm 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2073
Location: Weimar, Texas
Mike L wrote:


Your right. I was looking at so many tubes last night it all became a blur. The 6SQ7 seems more plentiful in metal. Still trying to find the last few parts. Can't seem to locate a source for the referenced trimmer cap (C5) Digi-Key had some but had to buy in bulk =$. Also looking for cap C9 with the correct spacing. The board looks tight so not sure how much wiggle room there will be.


Here's a shot of the board I built. You can see that some parts weren't quite as specified.

Image

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Sun 22, 2017 5:46 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
Not having much luck finding a trimmer cap (C5) Sprague Goodman (GMC30500 or GMC30600) 50-200pf or similar. Anyone know of a source? I did find this place; link below, but have never ordered anything from them. As usual can't seem to get everything from one source. Shipping is a killer on parts worth pennies.

http://www.surplussales.com/index.html?.x=46&.y=8


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Mon 23, 2017 3:45 pm 
Member
User avatar

Joined: Aug Wed 26, 2009 1:50 am
Posts: 1573
Location: Mesquite NV 89027 (from Coventry, UK)
Mike L,

You should be OK ordering from Surplus Sales.

When I built mine I searched on eBay, and got lucky. Somebody had a couple of ceramic trimmer caps for sale at a reasonable price. Might be worth a try.

Edit: I found something here that might be suitable: http://danscloseoutsandspecialdeals.com ... overs.html

Scroll down until you find the Arco 20-250pF trimmer. This would probably work.

Colin


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Wed 25, 2017 2:24 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
Quote:
Edit: I found something here that might be suitable: http://danscloseoutsandspecialdeals.com ... overs.html


Colin, thanks for the info. I'll add it to my list of sources.


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Wed 25, 2017 4:14 am 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1311
Location: Albion, CA, USA, 95410
Ordered the PCB today. Now to round up parts...


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Thu 26, 2017 12:11 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
Quote:
Ordered the PCB today. Now to round up parts...


It is a really nice board. Still have a couple small parts to source and a couple non-radio projects to finish and then can start construction.


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Tue 31, 2017 3:34 am 
Member

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1311
Location: Albion, CA, USA, 95410
Got the PCB and it looks nice. Digging through my stash I found two NOS variable caps that measure around 200pF and look like they will fit. Mike, if you still need one let me know. I need to look through my junk and then figure out what else I need to order.


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Feb Thu 02, 2017 1:28 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
madlabs wrote:
Got the PCB and it looks nice. Digging through my stash I found two NOS variable caps that measure around 200pF and look like they will fit. Mike, if you still need one let me know. I need to look through my junk and then figure out what else I need to order.



PM sent


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Feb Sun 05, 2017 11:55 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
Solamar wrote:
BobWeaver wrote:
Polarity doesn't matter on those inductors.

The first thing I'd check is to make sure the boost converter part of the circuit is working, and check with a voltmeter that you are getting the required high voltage.


(Humble Pie) - You are completely correct. No matter how you "clock" the 4 pin inductors, the contacts will cross pins 2 and 4.

I should have my replacement inductors today and will reinstall and continue troubleshooting. Boost converter is working correctly and B+ voltages are high enough to bring the led to full brightness. Think it is something on the RF side.


Working on my board today. Going along nicely, however I'm not sure about the inductors. The spacing is such that there is only two ways it can be inserted. So does it matter then? The data sheet references to pin numbers but there are none. The board has a dot near one of the lead holes which I assume is pin 1 but the inductor is not marked. The first photo is the inductor upside down. Two of the pins have what looks like a lead attached. It will clock two different ways on the board. So are pins 1 and 3 irrelevant as far as their position?


Attachments:
IMG_1154.jpg
IMG_1154.jpg [ 46.29 KiB | Viewed 6007 times ]
IMG_1153.jpg
IMG_1153.jpg [ 74.86 KiB | Viewed 6007 times ]
Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Feb Mon 06, 2017 2:12 am 
Member
User avatar

Joined: Mar Tue 13, 2012 6:56 am
Posts: 1063
Location: San Diego
Mike L wrote:
Two of the pins have what looks like a lead attached. It will clock two different ways on the board. So are pins 1 and 3 irrelevant as far as their position?

Yes. Since the leads are on the diagonal pins, rotating by 180° will not make any difference.

Attachment:
inductor.jpg
inductor.jpg [ 27.6 KiB | Viewed 5996 times ]

Matt


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Feb Sat 18, 2017 1:27 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
I have the board completed and powered it up, but the led barely glows and then begins to pulsate. I pulled the 6888 tube suspecting I had inserted it wrong as the tube I bought (unknowingly) had the key locating pin broken off. Powered up the board without the 6888 and the led powered normally along with the 6SQ7 filament glowing. Verified correct voltage on pins 2 and 7 of the socket for the 6888 and had 6 volts. Verified that I had the tube inserted correctly as pins 2 and 7 were the only ones with continuity and there is a telltale indication on the base as to where the key was, so made sure they went into the correct socket locations. Powered up again with the same result. Thinking that the 6888 was pulling everything down I put the 6888 in my emission tube tester and it passed all tests. Any idea what's going on here.


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Feb Sun 19, 2017 4:05 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
Guess I'll get another tube and give it another try. Running out of time for projects with a move coming and will need to pack everything up.


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Feb Mon 20, 2017 5:29 am 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 23566
Location: Somers, CT
Could it be your power supply can't handle the full load?

Pete

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Feb Tue 21, 2017 1:38 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
Peter Bertini wrote:
Could it be your power supply can't handle the full load?

Pete


Pretty sure its not the power supply. I ordered the same one on the parts list. I also checked it with just the 6888 tube installed and had the same issue. So it should be the tube or the circuit for that tube. Visually everything is soldered correctly, but there could be a defective component. Given the tube had a broken alignment pin I suspect the tube to be the issue. Should have a replacement in a couple days.


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Feb Sat 25, 2017 11:18 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
Mike L wrote:
Guess I'll get another tube and give it another try. Running out of time for projects with a move coming and will need to pack everything up.


As it turns out, it wasn't the tube at all. Tried another tube with the same result. Well this time I left it on longer and eventually the led got brighter and so did the tube filaments. I don't know why I was thinking that it would be instant power on....hey it has tubes that need to warm up dummy me! :oops:

Well its up and operating with a very strong signal. At times too strong. had to move it to the basement and play with the volume input and modulation to get a undistorted audio output. :D. I sure like this more than the Lil 7 I built earlier.


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Feb Sat 25, 2017 11:36 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14047
Congratulations!!!

The 6888 in any form is no doubt a fine example of a homebrew transmitter, but I'm especially partial to the versions with preamp...


Tom


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: May Sat 06, 2017 2:17 pm 
Member

Joined: Mar Sun 01, 2015 10:10 pm
Posts: 48
Location: Pittsburgh, Pennsylvania
I just went through my Digikey packing list with my order and the schematic, and I finally have everything except the tubes. Very nicely made PCB, compared to the old arcade game PCBs I am used to working on. lol. Hoping to find the tubes soon.

It looks like a fun build...I hope I don't run into problems.

Jeff


Top
 Profile  
 
 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Thu 24, 2017 2:24 pm 
Member
User avatar

Joined: May Fri 25, 2012 3:31 am
Posts: 514
Location: Clayton, Ind.
This may belong elsewhere, but does this really draw 2 amps? If not, what size transformer will work?

_________________
TDane WA9YI

Radio is a divine gift; God made us able to do one thing while listening to another.


Top
 Profile  
 
Post New Topic Post Reply  [ 131 posts ]  Go to page Previous  1 ... 3, 4, 5, 6, 7  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 4 guests



Search for:
Jump to:  






























-->


Privacy Policy :: Powered by phpBB