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


It is currently Sep Wed 23, 2020 7:10 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 16 posts ] 
Author Message
 Post subject: first amp to build 60fx5 (2)
PostPosted: Jan Wed 01, 2020 5:19 pm 
Member

Joined: Nov Wed 08, 2017 3:28 pm
Posts: 53
Attachment:
s-l1600.jpg
s-l1600.jpg [ 325.96 KiB | Viewed 1932 times ]


I'm wrapping up building the 6888 transmitter with amplification. I enjoyed the work so much I'd like to build a simple amplifer for these reasons:

1 Hobby enjoyment
2 to run an early 90's discman to speakers or one speaker to hear it loud enough to hear while working on remodling projects I'll be working on next month.
3 I'd like to build a more powerful and complex amplifier eventually, but I'm fairly green and this looks like a good starter project to get my skills up to speed some

so I'l like your folk's imput on a couple of things:

1 I would like to add a gain control (volume control) to the circuit as the line out of the cd player doesn't have volume control and I really don't want to use the headset output if I can help it. I checked another topic from awhile back and it was suggested to add a small pre amp with a pot as the best option, but the photo program used was expired for the schmatics and is unavailable. What do you guys think?

2 what range of speakers would work with this type of set up? I have a few to chose from and would eventually like to have something to run two good 6 x 9's I have just collecting dust. I suspect this amp is not powerful enough for those and that is okay, but would like a decent range.

thank you for any responses,
Jeff


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Wed 01, 2020 5:25 pm 
Member

Joined: Nov Wed 08, 2017 3:28 pm
Posts: 53
I just looked over the schematic I posted and it is a different version than the one I was studying before. Looks like it has a gain control built in but the inputs are different. would I be able to put in a standard stereo input into this?

Jeff


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Wed 01, 2020 6:07 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 26465
Location: Detroit, MI USA
Yes, but......

This circuit was designed for an entry level phonograph which used a "high" output cartridge, probably on the order of 3 volts or so. This worked perfectly well when mated up with such a cartridge.

The line or headphone outputs of modern electronic devices are nowhere near 3 volts, so some sort of additional gain before the input of this is required. There are simple preamp circuits floating around to add another stage. Due to the fact that the two 60FX5 tube filaments in series already adds up to 120 volts, you can't easily add another tube to this circuit to serve as the preamp.

Also, it was probably used to drive relatively small speakers, I think that the average 6 x 9 speaker may be a bit too much for the low 1 watt output of this amplifier should you ever intend to go there. You might be able to get away with a really efficient 4" or 5" speaker on this amp though.

I think we can come up with a simple amplifier circuit that puts out just a bit more power, maybe on the order of 2 watts, and has a built in preamp. It can be done with 3 tubes, something like 2 50C5's or 50L6's and a 12AX7.

Also, this amplifier and most simple ones have common connection from their input returning to the power line (even if done through a resistor-capacitor network like the one shown) making them somewhat dangerous. This particular one would have originally been completely enclosed inside the cabinet of a phonograph with no possibility of contacting any part of the circuit, and no input connections that any external device could have been plugged into.

You may want to consider adding a dedicated isolation transformer to the design, or better yet build a fully transformer powered amplifier. There are plenty of good circuits around or you could copy a commercially built amplifier.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Wed 01, 2020 6:26 pm 
Member

Joined: Nov Wed 08, 2017 3:28 pm
Posts: 53
Thank you for the quick reply. I will hit the drawing board and keep looking for a different schematic. Either way, I would employ the use of a power transformer for safety reasons.


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Wed 01, 2020 11:19 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4071
I built Larry Lisle's 60FX5 stereo amp which requires four tubes (push-pull).

Full article here, scroll down: viewtopic.php?f=12&t=233034

It uses a 1:3 step up transformer at the input and my CD player plays it plenty loud with 6" speakers. It's about 2 watts. I'm intrigued by the simplicity of the circuit you posted. Lisle and I corresponded and he was very impressed with the sound after reconfiguring his amp to be single ended, like in your posted circuit.

Instead of the line out of your CD player, why not use the headphone jack? If so, you may want to put 32 ohm resistors in parallel with each channel instead of using an input transformer.

All this is to say is, why not breadboard the amp and use a step up transformer at the input?


Last edited by Macrohenry on Jan Thu 02, 2020 12:10 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Wed 01, 2020 11:31 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4071
Here's another simple circuit. Google "lighthouse 6bm8" for more.

I built mine using Altec Lansing line transformers as output transformers. They are not single ended trannys, but they don't come close to saturating when driven by the 6BM8, so they sound wonderful. I like to use an external power supply to eliminate two sources of hum.


Attachments:
lighthouse.jpg
lighthouse.jpg [ 91.8 KiB | Viewed 1886 times ]
6BM8black800.jpg
6BM8black800.jpg [ 81.3 KiB | Viewed 1886 times ]
Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Thu 02, 2020 12:16 am 
Member
User avatar

Joined: Sep Wed 10, 2014 7:13 pm
Posts: 1169
Location: Urbana, Illinois
Macrohenry wrote:
Here's another simple circuit. Google "lighthouse 6bm8" for more.

I built mine using Altec Lansing line transformers as output transformers. They are not single ended trannys, but they don't come close to saturating when driven by the 6BM8, so they sound wonderful. I like to use an external power supply to eliminate two sources of hum.
+1 on singled-ended amplifiers using the 6BM8.

The triode section of the 6BM8 provides the necessary additional voltage gain for typical “line level” audio signals which are usually in the range of 150mV to 250mV.

When I was 12 years old my parents gave me a reel-reel tape recorder for Christmas. The brand name on it was “The Elizabethan”
Attachment:
96DF5F37-987E-4C7C-ABD7-4A7B6D14ACAD.jpeg
96DF5F37-987E-4C7C-ABD7-4A7B6D14ACAD.jpeg [ 368.65 KiB | Viewed 1880 times ]
It was made by Collaro (UK).
It sounded terrific for an inexpensive mono reel-reel.

Its audio amplifier section used a 6BM8.

It had a 5x7 inch British speaker in it, which also sounded terrific.

-EB

_________________
I’m learning to be a leading-edge designer of trailing-edge technology.


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Thu 02, 2020 4:44 am 
Member
User avatar

Joined: Sep Mon 16, 2013 2:42 am
Posts: 4172
Location: Tucson, Arizona U.S.A.
Try the speakers you have with whatever amp you build. It won't hurt anything and you may find that all of them work OK. Besides the amplifier and the speaker, it also depends on your room and how loud you want to play it. Larger speakers frequently need less power than smaller ones since they can move more air. But it depends on the cabinet they are mounted in. The only way to tell is to try it.

What type of CD player do you have? The AC powered ones have considerably higher output voltage than the battery powered ones. The line output will probably be higher than the headphone output.

If you build an AC/DC amplifier like the schematic you posted, be sure to run it from an isolation transformer to eliminate the shock hazard from the external connections (the internal wiring is still dangerous).

_________________
Jim Mueller


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Thu 02, 2020 4:50 am 
Member

Joined: Nov Wed 08, 2017 3:28 pm
Posts: 53
Good information. To be honest, it might be a good idea to buy a book. I see a couple on Ebay I'm interested in. I thought finding an amplifier schematic would be much simpler. I am more interested in building than designing.


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Thu 02, 2020 5:03 am 
Member

Joined: Nov Wed 08, 2017 3:28 pm
Posts: 53
The CD player is a Sony D-33. Works really well other than there is no skip protection.


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Thu 02, 2020 10:40 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11629
There are stereo 50C5 amps in most any tube manual from late 50s up. Usually have a 12AX7 preamp but a pair of 12AV6 will give same results.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Mon 13, 2020 6:24 am 
Member
User avatar

Joined: Dec Sat 24, 2011 9:17 pm
Posts: 6508
Location: Vancouver Island, Canada
j8000 wrote:
Good information. To be honest, it might be a good idea to buy a book. I see a couple on Ebay I'm interested in. I thought finding an amplifier schematic would be much simpler. I am more interested in building than designing.
Right, no need to reinvent the wheel, altho new ideas do crop up on rare occasions.

You can often substitute different tubes into a proven design with minimal or even no alterations to the schematic.
50C5 tubes or 50L6 are common and cheap and work well with low plate voltage. Also you can use output transformers from cheap AA5 radios.
If you decide on push-pull, you need to buy an output transformer with a center tap, but it only needs to handle 3 watts or so, and those are pretty cheap.

_________________
Watch the doughnut, not the hole.
Burl Ives, RIP, oldtimer.
[:l>)


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Mon 13, 2020 8:55 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 7:13 pm
Posts: 1169
Location: Urbana, Illinois
The first amplifier I built from scratch had 4 tubes.

There was a 12SQ7, 50L6, and 35Z5. This portion was a direct copy of the audio stages and power supply of a standard AA5 radio. But because I wanted to use this amplifier with a microphone, I added a preamplifier stage using a 12SJ7 pentode, which gave me plenty of voltage gain. My microphone was a handheld unit fully encased in plastic, so I felt it was safe to use it with an AC/DC non-isolated amplifier.

One of my applications was a “hidden loudspeaker” that I could put into an unexpected place and then talk through it. I think I got the idea from an episode of the “Candid Camera” TV show.

I made a little plywood box just big enough to hold a 4” speaker that I took from a discarded radio. The output transformer was riveted to the speaker. I left it in place. Because I was feeding the speaker at the high impedance of the primary (2500 ohms), I used a twisted pair of 26 gauge magnet wire for the connecting cable between my amplifier and the hidden speaker. It was almost invisible. Sometimes the place where I hid the speaker was 50 feet away from the amplifier and microphone.

I had a lot of fun with it. I think I was about 12 years old when I built it.

-EB

_________________
I’m learning to be a leading-edge designer of trailing-edge technology.


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Thu 16, 2020 7:04 pm 
Member

Joined: Nov Wed 08, 2017 3:28 pm
Posts: 53
that's great.

I have been reading the book I ordered. I think I'm going to head in the direction of a good pre-amp, power supply and tone controls all in stereo. Then start with a modest 8 or so watt power amplifier and go from there.


I question I want to ask is most designs I've seen call for RCA jacks for the imput. I'd prefer the standard stereo jacks. Are the RCA's more superior?

Jeff


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Fri 17, 2020 1:20 am 
Member
User avatar

Joined: Dec Sat 24, 2011 9:17 pm
Posts: 6508
Location: Vancouver Island, Canada
RCA jacks are easy to clean, easy to get a good connection.
You can shop for high-end gold plated RCA cords at any thrift store.
Your amp could have both types of input jacks.

For 8 Watts, you are going to need a power transformer with a 6 volt secondary for the power tube heaters and a high voltage something like 300 volts secondary for the plate voltage (B+).
Start by choosing the tubes, and then we can help you choose 3 transformers, one for power and two for stereo output.

The amps at the start of this thread were low power, 3 to 5.5 Watt with 110 volts on the plates. With those designs, you can skip the expensive power transformer and maybe run them straight from the wall outlet with a bit of isolation, wall wart transformers.

Building from scratch is fun, but costly. If you just need an amp to work on and learn from, buying a used one and refurbishing it is a good move, chassis with sockets and controls.

_________________
Watch the doughnut, not the hole.
Burl Ives, RIP, oldtimer.
[:l>)


Top
 Profile  
 
 Post subject: Re: first amp to build 60fx5 (2)
PostPosted: Jan Fri 17, 2020 1:59 am 
Member
User avatar

Joined: Sep Mon 16, 2013 2:42 am
Posts: 4172
Location: Tucson, Arizona U.S.A.
RCA jacks ARE the standard audio connectors.

_________________
Jim Mueller


Top
 Profile  
 
Post New Topic Post Reply  [ 16 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 8 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB