There are several options for building your first amplifier.
You will have to decide which choice is right for you based on the needed power, complexity, and expense. These kits and amplifiers built up from circuit boards, can range in price from a modest cost of $139.50, to $1,000 or more without an enclosure.

Here is a list of choices:

1.) A Push Pull 11BM8 pentode kit that includes everything except chassis: Look under kits-audio, # K-508

https://secure.tubesandmore.com/

2.) A Push Pull ECL82 pentode for 9 watts per channel: Stoetkit Jr.
This is a complete kit that includes everything needed, to include chassis, but is not cheap. This is a fine sounding amplifier.

http://www.stoetkit.nl/stoetkit_junior.php

3.) There are two choices here, 2A3 and 300B SET that includes all needed items, to include chassis. The Paramour, or Paramount:

http://www.bottlehead.com/et/et.html

4.) There are several choices here, from a Push Pull 6V6 pentode at 10 watts per channel. To single ended 6550 pentode, and 300B/2A3 set amplifiers that include all items needed, to include chassis.
These kits can be pretty expensive, it is according to what parts and trtansformer quality level that you choose.

http://audionotekits.espyderweb.net/

5.) There are three power level options here of Push Pull pentode amplifier circuit boards. You will have to source all of the needed components and chassis for this offering. But, I feel you will learn more here than about any other way of starting out, short of a complete DIY effort from a schematic. Dynaco ST35 and ST70 clones, and EICO EF89 clone circuit boards, there are many choices of output tubes available from these basic boards, to include 6B4G or 2A3 triode:

http://www.diytube.com/phpBB2/index.php

6.) This is a universal circuit board that can help you obtain several Push Pull amplifer configurations using different pentode vacuum tubes, like the KT88, EL34, 6L6G. But, it gives you the option of using a triode vacuum tube such as the 6B4G/2A3, this is according to the output transfomer that you choose:

http://www.pmillett.com/push-pull_kt88_class_a_amp_with_universal_driver_pcb.htm

6.) There are a few choices here in SET amplifiers, and Push Pull pentode. Some people feel that Welborne Labs offers some of the best SET amplifer kits. Terraplane 300B, 45 Star Chief, and look under mods and modules for the Dynaco ST70 upgrade boards:

http://www.welbornelabs.com/

7.) There are more Dynaco pentode Push Pull circuit board offerings here, to include cloned transformers:

http://www.triodeelectronics.com/

8.) There are products here from circuit boards for Dynaco ST35 and ST70 amplifiers, to complete kits:

http://www.tubes4hifi.com/parts.htm

9.) There are several Dynaco offerings here, from bare circuit boards, to completely stuffed circuit boards and kits:

http://www.curcioaudio.com/

10.) There are several kits here, from Push Pull pentode amplifiers, to SET amplifiers:

http://www.diyhifisupply.com/index.htm

You will find that many of these sources have discussion forums like here, that will help guide you in making the right kit choice, and in building that kit.

Here are a few sources for chassis for your new project:

1.) Design Build Listen: http://www.designbuildlisten.com/

2.) Dynaco ST70 and MKIII pre-punched chassis:

http://cgi.ebay.com/Two-New-Dynaco-MKIII-Chassis-Mark-III-MK-Dynakit_W0QQitemZ5861170048QQcategoryZ50593QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

3.) Par-Metal: http://www.par-metal.com/

Output transformers:

1.) Hammond SET and Push Pull: http://www.hammondmfg.com/

2.) EDCOR X-type: http://www.edcorusa.com
3.) Heyboer transformers: http://www.heyboertransformers.com/

4.) Silk Transformers, PP and SET types:

http://www.sacthailand.com/Engfirstpage.html

5.) James Transfomers at Euphonia Audio:

http://www.euphoniaaudio.com/ea/nfoscomm/catalog/

6.) Lundhal Transfomers at K&K audio: http://www.kandkaudio.com/

7.) Magnequest Transformers: http://www.magnequest.com/home.htm

8.) Electra Print Transformers: http://www.electra-print.com/

I suggest that you access these many forums and start reading.

Also, the many other amplifier sources here are run by very nice people who will be glad to answer your questions in helping you make the right amplifier choice.

Good Luck

Norris Wilson